feat：添加对话情景功能

frontend/src/lib/errors.ts

@@ -3,7 +3,7 @@
 // 来源：docs/03-接口文档.md §五 错误码
 // ============================================================
 
-import type { ErrorCode } from "../types";
+// ErrorCode type reserved for future use
 
 /** 将错误码转为用户友好文案（需要传入翻译函数） */
 export function getErrorMessage(code: string, translate: (key: string) => string): string {

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",

frontend/src/lib/i18n/ja-JP.ts

@@ -26,6 +26,21 @@ export const jaJP: TranslationMap = {
   "settings.detail.high": "高",
   "settings.language": "言語",
   "settings.language.desc": "インタラクション言語の設定",
+  "settings.scenario": "シナリオ",
+  "settings.scenario.desc": "AIの役割を選択",
+
+  // Scenarios
+  "scenario.choose": "シナリオを選択",
+  "scenario.freeChat": "フリーチャット",
+  "scenario.freeChat.desc": "AIビジュアルアシスタントと自由に会話",
+  "scenario.interviewer": "模擬面接官",
+  "scenario.interviewer.desc": "AIが面接官として模擬面接を実施",
+  "scenario.englishTeacher": "英語の先生",
+  "scenario.englishTeacher.desc": "AI英語教師が文法を修正し会話を導く",
+  "scenario.debate": "ディベート相手",
+  "scenario.debate.desc": "AIがあなたの观点に反論し論理的思考を鍛える",
+  "scenario.interpreter": "同時通訳",
+  "scenario.interpreter.desc": "リアルタイムで中日相互翻訳",
 
   // Video indicators
   "video.observing": "👁️ 観察中",
@@ -63,6 +78,7 @@ export const jaJP: TranslationMap = {
   "chat.userLabel": "あなた",
   "chat.input.placeholder": "メッセージを入力...",
   "chat.send": "送信",
+  "chat.scenarioSwitched": "{name} モードに切り替えました",
 
   // Session messages
   "session.changeDetected": "👁️ シーン変化を検出",

frontend/src/lib/i18n/zh-CN.ts

@@ -26,6 +26,21 @@ export const zhCN: TranslationMap = {
   "settings.detail.high": "高",
   "settings.language": "语言",
   "settings.language.desc": "交互语言偏好",
+  "settings.scenario": "对话情景",
+  "settings.scenario.desc": "选择 AI 扮演的角色",
+
+  // Scenarios
+  "scenario.choose": "选择对话情景",
+  "scenario.freeChat": "自由对话",
+  "scenario.freeChat.desc": "AI 视觉助手，自由聊天",
+  "scenario.interviewer": "模拟面试官",
+  "scenario.interviewer.desc": "AI 扮演面试官，进行模拟面试",
+  "scenario.englishTeacher": "英语老师",
+  "scenario.englishTeacher.desc": "AI 英语外教，纠正语法并引导对话",
+  "scenario.debate": "辩论对手",
+  "scenario.debate.desc": "AI 反驳你的观点，锻炼逻辑思维",
+  "scenario.interpreter": "同声翻译",
+  "scenario.interpreter.desc": "实时中英互译，口语化翻译",
 
   // Video indicators
   "video.observing": "👁️ 观察中",
@@ -63,6 +78,7 @@ export const zhCN: TranslationMap = {
   "chat.userLabel": "你",
   "chat.input.placeholder": "输入文字对话...",
   "chat.send": "发送",
+  "chat.scenarioSwitched": "已切换到 {name} 模式",
 
   // Session messages
   "session.changeDetected": "👁️ 画面变化检测",

frontend/src/lib/scenarios.ts

@@ -0,0 +1,47 @@
+// ============================================================
+// scenarios — 对话情景定义
+// 职责：定义预置情景的展示数据和交互行为
+// 注意：system prompt 由后端 scenarios.go 管理，此处仅定义 UI 展示数据
+// ============================================================
+
+export interface Scenario {
+  id: string;
+  icon: string;
+  nameKey: string;       // i18n key
+  descKey: string;       // i18n key
+  defaultLanguage?: string;  // 可选：切换情景时自动设置的语言
+}
+
+export const scenarios: Scenario[] = [
+  {
+    id: "free_chat",
+    icon: "💬",
+    nameKey: "scenario.freeChat",
+    descKey: "scenario.freeChat.desc",
+  },
+  {
+    id: "interviewer",
+    icon: "🎯",
+    nameKey: "scenario.interviewer",
+    descKey: "scenario.interviewer.desc",
+  },
+  {
+    id: "english_teacher",
+    icon: "📚",
+    nameKey: "scenario.englishTeacher",
+    descKey: "scenario.englishTeacher.desc",
+    defaultLanguage: "en-US",
+  },
+  {
+    id: "debate",
+    icon: "⚔️",
+    nameKey: "scenario.debate",
+    descKey: "scenario.debate.desc",
+  },
+  {
+    id: "interpreter",
+    icon: "🌐",
+    nameKey: "scenario.interpreter",
+    descKey: "scenario.interpreter.desc",
+  },
+];

frontend/src/lib/storage.ts

@@ -15,6 +15,7 @@ const DEFAULT_CONFIG: SessionConfig = {
   ttsEnabled: true,
   detailLevel: "low",
   language: "zh-CN",
+  scenario: "free_chat",
 };
 
 /** 加载配置，无存储时返回默认值 */