feat: 支持多语言提示词本地化和界面优化

- 添加 prompt_locale 参数支持简体中文、繁体中文和英文提示词本地化
- 移除内置 agents 配置以简化系统架构
- 更新 ContextBuilder 使用动态提示词模板而非硬编码内容
- 在 AgentLoop、Web 接口和 AgentService 中传递 locale 参数
- 添加输出语言指令确保用户界面内容按指定语言生成
- 扩展前端 LanguageSwitcher 组件支持三种语言选项
- 优化 Header 和侧边栏组件的响应式布局和文本截断处理
- 更新测试用例验证不同语言环境下的提示词正确性

app-instance/backend/tests/unit/test_websocket_chat.py

@@ -73,6 +73,7 @@ def test_websocket_message_returns_chat_metadata_and_session_updated() -> None:
                 {
                     "type": "message",
                     "content": "hello",
+                    "prompt_locale": "zh-Hant",
                     "metadata": {"source": "test"},
                     "attachments": [{"file_id": "file-1", "name": "a.txt"}],
                 }
@@ -89,6 +90,7 @@ def test_websocket_message_returns_chat_metadata_and_session_updated() -> None:
             "user_id": None,
             "title": None,
             "execution_context": None,
+            "prompt_locale": "zh-Hant",
             "model": None,
             "provider_name": None,
             "embedding_model": None,
@@ -134,6 +136,7 @@ def test_websocket_message_uses_direct_processing_when_loop_is_not_running() ->
             "user_id": None,
             "title": None,
             "execution_context": None,
+            "prompt_locale": None,
             "model": None,
             "provider_name": None,
             "embedding_model": None,
@@ -149,7 +152,10 @@ def test_rest_chat_uses_direct_processing_when_loop_is_not_running() -> None:
     app = create_app(service=service, manage_service_lifecycle=False)
 
     with TestClient(app) as client:
-        response = client.post("/api/chat", json={"session_id": "web:alpha", "message": "hello"})
+        response = client.post(
+            "/api/chat",
+            json={"session_id": "web:alpha", "message": "hello", "prompt_locale": "en"},
+        )
 
     assert response.status_code == 200
     assert service.calls == [
@@ -160,6 +166,7 @@ def test_rest_chat_uses_direct_processing_when_loop_is_not_running() -> None:
             "user_id": None,
             "title": None,
             "execution_context": None,
+            "prompt_locale": "en",
             "model": None,
             "provider_name": None,
             "embedding_model": None,