feat(voice): 实时语音对话页（React 完全复刻原版 UI）

- /voice 页面：中间圆球 + 左右按钮 + 状态图标 + 右下角气泡（进场/淡出/阶梯字号/上限8）+ 噪声门弧线电平，结构类名与原版一致
- s2s WebSocket 客户端 + worklet 音频（mic-capture/audio-playback）+ orb 可视化
- 摄像头实时预览（默认开启）+ 视觉识别状态条（后端 YOLO 推理）
- 底部园区概览条（复用 ParkOverviewStrip），orb-wrap 视窗居中
- 页眉复用 ScreenLayout；左右键导航加入 /voice
- 文档：docs/voice-integration-plan.md

public/voice-demo/ui/dom.js

@@ -0,0 +1,37 @@
+// @ts-check
+/** Small shared helpers used across the UI modules: a strict query selector,
+ *  HTML escaping for text we drop into innerHTML, error-string trimming, and
+ *  the opt-in debug flag. */
+
+/** Opt-in tracing: `localStorage.setItem("s2s.debug", "1")` then reload. */
+export const DEBUG = (() => {
+  try {
+    return localStorage.getItem("s2s.debug") === "1";
+  } catch {
+    return false;
+  }
+})();
+
+/**
+ * Query a single element, throwing if it's missing (so a broken selector fails
+ * loudly at startup rather than as a later null-deref).
+ * @template {HTMLElement} T
+ * @param {string} selector
+ * @returns {T}
+ */
+export function $(selector) {
+  const el = document.querySelector(selector);
+  if (!el) throw new Error(`Missing element: ${selector}`);
+  return /** @type {T} */ (el);
+}
+
+/** @param {string} s @returns {string} */
+export function escHtml(s) {
+  return s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
+}
+
+/** Trim a long error message to fit the orb caption. @param {string} text */
+export function truncateError(text) {
+  if (text.length <= 90) return text;
+  return text.slice(0, 87) + "…";
+}