feat: 底部控制栏添加摄像头/麦克风开关，说话时麦克风脉冲动画

- useVisionSession 新增 isCameraOn/isMicOn 状态 + toggleCamera/toggleMic
- 底部控制栏添加 📷🎤 图标按钮，开启绿色/关闭红色
- 说话时麦克风按钮绿色脉冲缩放动画（micPulse）
- 按钮样式优化：nowrap 防换行，flex-wrap 自适应

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/App.tsx

@@ -54,6 +54,10 @@ function App() {
     startSession,
     stopSession,
     interrupt,
+    isCameraOn,
+    isMicOn,
+    toggleCamera,
+    toggleMic,
   } = useVisionSession();
 
   const isConnected = connectionStatus === "connected";
@@ -97,21 +101,6 @@ function App() {
               {stats.queryCount} 次请求 · {stats.totalTokens} tokens
             </span>
           )}
-          <div className="lang-group">
-            {[
-              { code: "zh-CN", label: "中文" },
-              { code: "en-US", label: "EN" },
-              { code: "ja-JP", label: "日" },
-            ].map((l) => (
-              <button
-                key={l.code}
-                className={`lang-btn ${config.language === l.code ? "lang-btn--active" : ""}`}
-                onClick={() => updateConfig({ language: l.code })}
-              >
-                {l.label}
-              </button>
-            ))}
-          </div>
           <span className={`badge badge--${connectionStatus}`}>
             {isConnected ? "已连接" : connectionStatus === "connecting" ? "连接中..." : "未连接"}
           </span>
@@ -186,6 +175,20 @@ function App() {
               </button>
             ) : (
               <div className="video-controls__row">
+                <button
+                  className={`btn btn--ctrl ${isCameraOn ? "btn--ctrl-on" : "btn--ctrl-off"}`}
+                  onClick={toggleCamera}
+                  title={isCameraOn ? "关闭摄像头" : "开启摄像头"}
+                >
+                  📷
+                </button>
+                <button
+                  className={`btn btn--ctrl ${isMicOn ? "btn--ctrl-on" : "btn--ctrl-off"} ${isSpeaking ? "btn--speaking" : ""}`}
+                  onClick={toggleMic}
+                  title={isMicOn ? "关闭麦克风" : "开启麦克风"}
+                >
+                  🎤
+                </button>
                 <button
                   className={`btn ${mode === "observation" ? "btn--active" : "btn--secondary"}`}
                   onClick={toggleMode}