refactor: 弱化媒体播放控制区 + MQTT 客户端 ID 唯一化

播放控制区：
- 从底部中央移到右下角，整体缩小（播放键 42→30px、导航键 34→26px）
- 背景更透（0.8→0.55）、阴影更轻，视觉弱化不抢内容
- 播放名不再显示完整地址：URL 媒体只显示文件名（cleanName 清洗，去掉协议/路径/查询）

MQTT 客户端 ID：
- 后端 client_id 由固定 dpm-backend 改为 dpm-backend-{pid}-{随机}，多实例不互踢
- 前端 client_id 增加时间戳 + 更高熵随机，避免多屏/多标签竞争

src/styles/mediascreen.css

@@ -109,31 +109,32 @@
   border-bottom: 1px solid rgba(47, 107, 255, 0.3);
 }
 
-/* 中央播放控制层（悬浮） */
+/* 右下角轻量播放控制（弱化悬浮） */
 .ms-controls {
   position: absolute;
-  left: 50%;
-  bottom: 22px;
-  transform: translateX(-50%);
+  right: 16px;
+  bottom: 14px;
+  left: auto;
+  transform: none;
   z-index: 10;
   display: flex;
   align-items: center;
-  gap: 16px;
-  padding: 10px 18px;
-  background: rgba(255, 255, 255, 0.8);
-  border: 1px solid rgba(120, 160, 220, 0.2);
-  border-radius: 40px;
-  backdrop-filter: blur(16px);
-  -webkit-backdrop-filter: blur(16px);
-  box-shadow: 0 12px 40px rgba(56, 100, 170, 0.18);
+  gap: 8px;
+  padding: 6px 12px;
+  background: rgba(255, 255, 255, 0.55);
+  border: 1px solid rgba(120, 160, 220, 0.16);
+  border-radius: 30px;
+  backdrop-filter: blur(12px);
+  -webkit-backdrop-filter: blur(12px);
+  box-shadow: 0 6px 22px rgba(56, 100, 170, 0.12);
   opacity: 0;
   transition: opacity 0.5s ease;
 }
 .ms-controls.visible { opacity: 1; }
 
 .ms-play {
-  width: 42px;
-  height: 42px;
+  width: 30px;
+  height: 30px;
   border-radius: 50%;
   border: none;
   display: flex;
@@ -142,7 +143,7 @@
   color: #fff;
   background: linear-gradient(140deg, var(--bd-blue, #2f6bff), var(--bd-cyan, #4cc2ff));
   cursor: pointer;
-  box-shadow: 0 6px 20px rgba(47, 107, 255, 0.4);
+  box-shadow: 0 4px 12px rgba(47, 107, 255, 0.3);
   transition: transform 0.2s;
 }
 .ms-play:hover { transform: scale(1.08); }
@@ -150,14 +151,14 @@
 .ms-nav {
   display: flex;
   align-items: center;
-  gap: 10px;
+  gap: 6px;
 }
 .ms-nav button {
-  width: 34px;
-  height: 34px;
+  width: 26px;
+  height: 26px;
   border-radius: 50%;
-  border: 1px solid rgba(47, 107, 255, 0.2);
-  background: rgba(255, 255, 255, 0.7);
+  border: 1px solid rgba(47, 107, 255, 0.18);
+  background: rgba(255, 255, 255, 0.6);
   color: var(--bd-blue, #2f6bff);
   display: flex;
   align-items: center;
@@ -172,32 +173,32 @@
 .ms-nav-num {
   display: inline-flex;
   align-items: baseline;
-  gap: 4px;
+  gap: 3px;
   font-family: "JetBrains Mono", "Oswald", monospace;
 }
 .ms-nav-num b {
-  font-size: 16px;
+  font-size: 13px;
   color: var(--bd-ink, #1d2c44);
 }
 .ms-nav-num em {
   font-style: normal;
-  font-size: 12px;
+  font-size: 10.5px;
   color: var(--bd-sub, #7d8fa9);
 }
 
 .ms-now {
   display: flex;
   align-items: center;
-  gap: 8px;
-  padding-left: 16px;
-  border-left: 1px solid rgba(47, 107, 255, 0.14);
+  gap: 6px;
+  padding-left: 10px;
+  border-left: 1px solid rgba(47, 107, 255, 0.12);
 }
 .ms-now-dot {
-  width: 8px;
-  height: 8px;
+  width: 6px;
+  height: 6px;
   border-radius: 50%;
   background: var(--bd-green, #17b26a);
-  box-shadow: 0 0 10px rgba(23, 178, 106, 0.8);
+  box-shadow: 0 0 8px rgba(23, 178, 106, 0.8);
   animation: msPulse 1.6s ease-in-out infinite;
 }
 @keyframes msPulse {
@@ -205,10 +206,10 @@
   50% { opacity: 0.4; transform: scale(0.75); }
 }
 .ms-now-name {
-  font-size: 13px;
-  font-weight: 600;
-  color: var(--bd-ink, #1d2c44);
-  max-width: 280px;
+  font-size: 11px;
+  font-weight: 500;
+  color: var(--bd-sub, #7d8fa9);
+  max-width: 160px;
   overflow: hidden;
   text-overflow: ellipsis;
   white-space: nowrap;
@@ -218,13 +219,13 @@
 .ms-sound {
   display: inline-flex;
   align-items: center;
-  gap: 7px;
-  padding: 8px 16px;
-  font-size: 12.5px;
+  gap: 6px;
+  padding: 5px 11px;
+  font-size: 11px;
   font-weight: 500;
   color: #4a5b76;
-  background: rgba(255, 255, 255, 0.85);
-  border: 1px solid rgba(47, 107, 255, 0.16);
+  background: rgba(255, 255, 255, 0.75);
+  border: 1px solid rgba(47, 107, 255, 0.14);
   border-radius: 30px;
   cursor: pointer;
 }