feat：添加对话情景功能

frontend/src/App.tsx

@@ -15,6 +15,7 @@ import { AuthPage } from "./components/AuthPage";
 import { AuthProvider, useAuth } from "./lib/auth";
 import { loadConfig, loadTheme, saveTheme } from "./lib/storage";
 import { I18nContext, parseLocale, t } from "./lib/i18n";
+import { scenarios } from "./lib/scenarios";
 import type { Locale } from "./lib/i18n";
 import type { Theme } from "./types";
 import "./App.css";
@@ -180,6 +181,27 @@ function AppContent() {
     sendTextMessage(prompt);
   }, [sendTextMessage]);
 
+  // ---- 情景选择 ----
+  const handleSelectScenario = useCallback((scenarioId: string) => {
+    const sc = scenarios.find(s => s.id === scenarioId);
+    const updates: Partial<import("./types").SessionConfig> = { scenario: scenarioId };
+    // 如果情景有默认语言，同步切换
+    if (sc?.defaultLanguage) {
+      updates.language = sc.defaultLanguage;
+    }
+    updateConfig(updates);
+    // 插入系统提示消息
+    const scenarioName = sc ? `${sc.icon} ${tr(sc.nameKey)}` : scenarioId;
+    setMessages(prev => [...prev, {
+      role: "system",
+      content: tr("chat.scenarioSwitched").replace("{name}", scenarioName),
+      timestamp: Date.now(),
+    }]);
+  }, [updateConfig, setMessages, tr]);
+
+  // 当前情景对象
+  const activeScenario = scenarios.find(s => s.id === (config.scenario || "free_chat")) || scenarios[0];
+
   // ---- 键盘快捷键 ----
   useEffect(() => {
     const handler = (e: KeyboardEvent) => {
@@ -443,6 +465,16 @@ function AppContent() {
           <div className="chat-panel-header">
             <span>{tr("chat.title")}</span>
             <div className="chat-panel-header__right">
+              <select
+                className="scenario-selector"
+                value={activeScenario.id}
+                onChange={(e) => handleSelectScenario(e.target.value)}
+                title={tr("settings.scenario")}
+              >
+                {scenarios.map((sc) => (
+                  <option key={sc.id} value={sc.id}>{sc.icon} {tr(sc.nameKey)}</option>
+                ))}
+              </select>
               {isConnected && mode === "observation" && (
                 <span className="chat-panel-header__mode">{tr("chat.mode.observation")}</span>
               )}
@@ -465,14 +497,16 @@ function AppContent() {
               messages={messages}
               currentReply={currentReply}
               connectionStatus={connectionStatus}
+              currentScenario={config.scenario}
               isProcessing={isProcessing}
               isVADReady={isVADReady}
-              vadError={vadError}
+              vadError={vadError ?? undefined}
               isMicOn={isMicOn}
               isSpeaking={isSpeaking}
               onSendText={sendTextMessage}
               onToggleMic={toggleMic}
               onSceneCard={handleSceneCard}
+              onSelectScenario={handleSelectScenario}
             />
           </div>
         </div>