feat：添加对话情景功能

frontend/src/lib/i18n/en-US.ts

@@ -26,6 +26,21 @@ export const enUS: TranslationMap = {
   "settings.detail.high": "High",
   "settings.language": "Language",
   "settings.language.desc": "Interaction language preference",
+  "settings.scenario": "Scenario",
+  "settings.scenario.desc": "Choose the AI's role",
+
+  // Scenarios
+  "scenario.choose": "Choose a scenario",
+  "scenario.freeChat": "Free Chat",
+  "scenario.freeChat.desc": "AI visual assistant, chat freely",
+  "scenario.interviewer": "Mock Interviewer",
+  "scenario.interviewer.desc": "AI plays interviewer for practice",
+  "scenario.englishTeacher": "English Tutor",
+  "scenario.englishTeacher.desc": "AI English tutor, corrects grammar",
+  "scenario.debate": "Debate Opponent",
+  "scenario.debate.desc": "AI challenges your viewpoints",
+  "scenario.interpreter": "Interpreter",
+  "scenario.interpreter.desc": "Real-time Chinese-English translation",
 
   // Video indicators
   "video.observing": "👁️ Observing",
@@ -63,6 +78,7 @@ export const enUS: TranslationMap = {
   "chat.userLabel": "You",
   "chat.input.placeholder": "Type a message...",
   "chat.send": "Send",
+  "chat.scenarioSwitched": "Switched to {name} mode",
 
   // Session messages
   "session.changeDetected": "👁️ Scene change detected",