fix: 管理后台连接状态 + 修复按钮无响应

连接状态（正式）：
- /api/display/state 扩展：screens_online（大屏心跳统计，opc/display/heartbeat）+ last_command（最近指令与发布结果）
- 前端大屏每 10s 上报心跳（稳定 client_id），后端 30s TTL 统计在线大屏数
- 管理台新增「连接状态」卡片：后端/MQTT/在线大屏/最近指令，3s 轮询刷新

按钮无响应根治：
- admin.js 改为 document 事件委托（data-nav/data-control/data-action/复制/预览），不再依赖逐个绑定
- /static 与 /admin 响应加 no-cache 头，杜绝旧 JS/CSS 缓存导致的按钮失效
- SSE 不再自动重载页面（避免与操作回调双重重载清掉反馈）；立即播放改为 toast 不重载

backend/static/admin.js

@@ -1,6 +1,7 @@
 /* =========================================================
    Admin 管理后台前端逻辑（Jinja 页面配套）
-   动态操作调用 FastAPI REST，完成后整页刷新（服务端重渲染）
+   事件采用 document 委托绑定，保证按钮点击稳定响应；
+   连接状态每 3s 轮询 /api/display/state 刷新
    ========================================================= */
 (function () {
   'use strict';
@@ -34,12 +35,12 @@
       })
       .catch(function () { toast('网络错误', 'error'); });
   }
-  function reload(msg) {
+  function reload(msg, delay) {
     if (msg) toast(msg);
-    setTimeout(function () { location.reload(); }, 350);
+    setTimeout(function () { location.reload(); }, delay || 600);
   }
 
-  /* ---------- 播放状态（SSE） ---------- */
+  /* ---------- 播放状态（SSE，仅更新状态文字，不自动重载页面） ---------- */
   var statusText = document.getElementById('statusText');
   try {
     var es = new EventSource('/api/events');
@@ -51,33 +52,118 @@
         else if (s.status === 'playing') statusText.textContent = '正在播放 — ' + s.name;
         else if (s.status === 'paused') statusText.textContent = '已暂停 — ' + s.name;
       }
-      if (msg.action === 'playlist_changed') reload();
     };
   } catch (err) { /* ignore */ }
 
-  /* ---------- 页面切换（MQTT 控制大屏） ---------- */
-  document.querySelectorAll('[data-nav]').forEach(function (btn) {
-    btn.addEventListener('click', function () {
+  /* =========================================================
+     连接状态轮询（/api/display/state）
+     ========================================================= */
+  var connEls = {
+    api: document.getElementById('connApi'),
+    mqtt: document.getElementById('connMqtt'),
+    screens: document.getElementById('connScreens'),
+    lastCmd: document.getElementById('connLastCmd'),
+  };
+  function setConn(id, ok, value) {
+    var el = connEls[id];
+    if (!el) return;
+    var dot = el.querySelector('.conn-dot');
+    var val = el.querySelector('.conn-value');
+    if (dot) dot.className = 'conn-dot ' + (ok ? 'on' : 'off');
+    if (val) val.textContent = value;
+  }
+  function pollStatus() {
+    fetch('/api/display/state', { cache: 'no-store' })
+      .then(function (r) { return r.json(); })
+      .then(function (d) {
+        setConn('api', true, '在线');
+        setConn('mqtt', !!d.mqtt_connected, d.mqtt_connected ? '已连接（' + (d.mqtt_host || '') + '）' : '未连接');
+        setConn('screens', (d.screens_online || 0) > 0, (d.screens_online || 0) + ' 台');
+        var lc = d.last_command;
+        if (lc) {
+          var names = { navigate: '页面切换', play: '播放', pause: '暂停', next: '下一项', prev: '上一项',
+            'play_target': '指定播放', alert: '通知', show_card: '卡片', set_mode: '播放模式' };
+          var when = new Date(lc.ts).toLocaleTimeString('zh-CN', { hour12: false });
+          setConn('lastCmd', !!lc.published,
+            (names[lc.action] || lc.action) + ' · ' + (lc.published ? '已广播' : '未广播') + ' · ' + when);
+        }
+      })
+      .catch(function () {
+        setConn('api', false, '离线');
+        setConn('mqtt', false, '未知');
+        setConn('screens', false, '未知');
+      });
+  }
+  if (connEls.api) { pollStatus(); setInterval(pollStatus, 3000); }
+
+  /* =========================================================
+     事件委托：页面切换 / 播放控制 / 媒体操作
+     ========================================================= */
+  document.addEventListener('click', function (e) {
+    var btn = e.target.closest ? e.target.closest('[data-nav], [data-control], [data-action], .copy-btn, [data-preview]') : null;
+    if (!btn) return;
+    e.stopPropagation();
+
+    // 预览
+    if (btn.hasAttribute('data-preview')) { openPreview(btn.closest('.media-card')); return; }
+
+    // 复制 URL
+    if (btn.classList.contains('copy-btn')) {
+      var url = btn.closest('.media-url').getAttribute('data-url') || '';
+      var full = /^https?:\/\//.test(url) ? url : window.location.origin + url;
+      var done = function () { toast('链接已复制'); };
+      if (navigator.clipboard && navigator.clipboard.writeText) {
+        navigator.clipboard.writeText(full).then(done).catch(function () { fallbackCopy(full); done(); });
+      } else { fallbackCopy(full); done(); }
+      return;
+    }
+
+    // 页面切换
+    if (btn.hasAttribute('data-nav')) {
       var page = btn.getAttribute('data-nav');
       post('/api/display/command', { action: 'navigate', params: { page: page } }, function () {
         toast('已切换大屏至「' + btn.textContent.trim() + '」');
       });
-    });
-  });
+      return;
+    }
 
-  /* ---------- 播放控制 ---------- */
-  document.querySelectorAll('[data-control]').forEach(function (btn) {
-    btn.addEventListener('click', function () {
+    // 播放控制
+    if (btn.hasAttribute('data-control')) {
       var action = btn.getAttribute('data-control');
-      if (action === 'minimize') {
-        post('/api/display/command', { action: 'minimize', params: {} });
-      } else {
-        post('/api/control', { action: action });
+      if (action === 'minimize') post('/api/display/command', { action: 'minimize', params: {} });
+      else post('/api/control', { action: action });
+      return;
+    }
+
+    // 媒体操作
+    if (btn.hasAttribute('data-action')) {
+      var card = btn.closest('.media-card');
+      var path = card.getAttribute('data-path');
+      var act = btn.getAttribute('data-action');
+      if (act === 'play-now') {
+        post('/api/playlist/play', { path: path }, function () { toast('已发送播放指令，大屏即将播放'); });
+      } else if (act === 'add-playlist') {
+        post('/api/playlist/add', { path: path }, function () { reload('已加入播放列表'); });
+      } else if (act === 'remove-playlist') {
+        post('/api/playlist/remove', { path: path }, function () { reload('已移出播放列表'); });
+      } else if (act === 'delete') {
+        if (!window.confirm('确定删除该文件？')) return;
+        post('/api/delete', { path: path }, function () { reload('已删除'); });
       }
-    });
+    }
   });
 
-  /* ---------- 播放设置 ---------- */
+  function fallbackCopy(text) {
+    var ta = document.createElement('textarea');
+    ta.value = text; ta.style.position = 'fixed'; ta.style.opacity = '0';
+    document.body.appendChild(ta); ta.select();
+    try { document.execCommand('copy'); } catch (err) { /* ignore */ }
+    document.body.removeChild(ta);
+  }
+
+  /* =========================================================
+     播放设置（change/input 事件）
+     ========================================================= */
   var playMode = document.getElementById('playMode');
   if (playMode) playMode.addEventListener('change', function () {
     post('/api/settings', { play_mode: playMode.value }, function () { toast('播放模式已更新'); });
@@ -105,20 +191,17 @@
 
   /* ---------- 显示控制 ---------- */
   var btnFullscreen = document.getElementById('btnFullscreen');
+  var btnAutostart = document.getElementById('btnAutostart');
   function renderDisplay() {
     if (btnFullscreen) btnFullscreen.textContent = fullscreen ? '切换窗口模式' : '切换大屏模式';
-    var btnAutostart = document.getElementById('btnAutostart');
     if (btnAutostart) { btnAutostart.textContent = autostart ? '已开启' : '已关闭'; btnAutostart.classList.toggle('active', autostart); }
   }
   if (btnFullscreen) btnFullscreen.addEventListener('click', function () {
-    fullscreen = !fullscreen;
-    renderDisplay();
+    fullscreen = !fullscreen; renderDisplay();
     post('/api/settings', { fullscreen: fullscreen });
   });
-  var btnAutostart = document.getElementById('btnAutostart');
   if (btnAutostart) btnAutostart.addEventListener('click', function () {
-    autostart = !autostart;
-    renderDisplay();
+    autostart = !autostart; renderDisplay();
     post('/api/settings', { autostart: autostart });
   });
   renderDisplay();
@@ -129,12 +212,10 @@
     var inp = document.getElementById('fileInput');
     var fileList = Array.from(inp.files || []);
     if (fileList.length === 0) { toast('请选择文件', 'error'); return; }
-
     var prog = document.getElementById('uploadProgress');
     var fill = document.getElementById('progressFill');
     var text = document.getElementById('progressText');
     prog.style.display = 'block';
-
     var done = 0;
     fileList.forEach(function (file) {
       var fd = new FormData();
@@ -167,7 +248,7 @@
     if (!url) { toast('请输入 URL', 'error'); return; }
     post('/api/media/add-url', { url: url }, function (d) {
       if (play) {
-        post('/api/playlist/play', { path: url }, function () { reload('已加入并开始播放'); });
+        post('/api/playlist/play', { path: url }, function () { toast('已加入并发送播放指令'); });
       } else {
         reload(d && d.duplicate ? 'URL 已存在于媒体库' : '已添加到媒体库');
       }
@@ -176,54 +257,15 @@
   if (btnAddUrl) btnAddUrl.addEventListener('click', function () { addUrlThen(false); });
   if (btnAddUrlPlay) btnAddUrlPlay.addEventListener('click', function () { addUrlThen(true); });
 
-  /* ---------- 复制资源 URL（FastAPI 输出） ---------- */
-  document.querySelectorAll('.copy-btn').forEach(function (btn) {
-    btn.addEventListener('click', function (e) {
-      e.stopPropagation();
-      var url = btn.closest('.media-url').getAttribute('data-url') || '';
-      var full = /^https?:\/\//.test(url) ? url : window.location.origin + url;
-      var done = function () { toast('链接已复制'); };
-      if (navigator.clipboard && navigator.clipboard.writeText) {
-        navigator.clipboard.writeText(full).then(done).catch(function () { fallbackCopy(full); done(); });
-      } else {
-        fallbackCopy(full); done();
-      }
-    });
-  });
-  function fallbackCopy(text) {
-    var ta = document.createElement('textarea');
-    ta.value = text; ta.style.position = 'fixed'; ta.style.opacity = '0';
-    document.body.appendChild(ta); ta.select();
-    try { document.execCommand('copy'); } catch (err) { /* ignore */ }
-    document.body.removeChild(ta);
-  }
-
-  /* ---------- 媒体操作（立即播放 / 加入播放 / 移出 / 删除） ---------- */
-  document.querySelectorAll('[data-action]').forEach(function (btn) {
-    btn.addEventListener('click', function (e) {
-      e.stopPropagation();
-      var card = btn.closest('.media-card');
-      var path = card.getAttribute('data-path');
-      var action = btn.getAttribute('data-action');
-      if (action === 'play-now') {
-        post('/api/playlist/play', { path: path }, function () { toast('正在播放'); });
-      } else if (action === 'add-playlist') {
-        post('/api/playlist/add', { path: path }, function () { reload('已加入播放列表'); });
-      } else if (action === 'remove-playlist') {
-        post('/api/playlist/remove', { path: path }, function () { reload('已移出播放列表'); });
-      } else if (action === 'delete') {
-        if (!window.confirm('确定删除该文件？')) return;
-        post('/api/delete', { path: path }, function () { reload('已删除'); });
-      }
-    });
-  });
-
-  /* ---------- 预览弹窗 ---------- */
+  /* =========================================================
+     预览弹窗
+     ========================================================= */
   var modal = document.getElementById('previewModal');
   var modalBody = document.getElementById('previewBody');
   var current = null;
 
   function openPreview(card) {
+    if (!card || !modal) return;
     var path = card.getAttribute('data-path');
     var type = card.getAttribute('data-type');
     var source = card.getAttribute('data-source');
@@ -246,11 +288,8 @@
     modal.style.display = 'none';
     current = null;
   }
-  document.querySelectorAll('[data-preview]').forEach(function (el) {
-    el.addEventListener('click', function () { openPreview(el.closest('.media-card')); });
-  });
   document.getElementById('previewClose').addEventListener('click', closePreview);
-  modal.addEventListener('click', function (e) {
+  if (modal) modal.addEventListener('click', function (e) {
     if (e.target === modal) closePreview();
   });
   document.addEventListener('keydown', function (e) { if (e.key === 'Escape') closePreview(); });
@@ -260,7 +299,7 @@
   });
   document.getElementById('previewPlay').addEventListener('click', function () {
     if (!current) return;
-    post('/api/playlist/play', { path: current.path }, function () { closePreview(); toast('正在播放'); });
+    post('/api/playlist/play', { path: current.path }, function () { closePreview(); toast('已发送播放指令'); });
   });
   document.getElementById('previewDelete').addEventListener('click', function () {
     if (!current) return;