fix(desktop): 修复桌面端 API 连接问题

- API 客户端使用完整后端 URL (localhost:3000)
- 添加 tauri-plugin-http 支持外部 HTTP 请求
- 配置 CSP 允许连接 localhost
- 同步 useChat hook 修复 WebSocket 错误处理

packages/desktop/src/api/client.ts

@@ -35,7 +35,8 @@ export interface HealthStatus {
   };
 }
 
-const API_BASE = '/api';
+// Tauri 应用需要完整的后端 URL
+const API_BASE = 'http://localhost:3000/api';
 
 async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
   const response = await fetch(`${API_BASE}${path}`, {
@@ -56,7 +57,11 @@ async function request<T>(method: string, path: string, body?: unknown): Promise
 
 // Health
 export async function getHealth(): Promise<HealthStatus> {
-  return request('GET', '/../health');
+  const response = await fetch('http://localhost:3000/health');
+  if (!response.ok) {
+    throw new Error(`HTTP ${response.status}`);
+  }
+  return response.json();
 }
 
 // Sessions
@@ -90,9 +95,8 @@ export async function sendMessage(
 
 // WebSocket
 export function createWebSocket(sessionId: string): WebSocket {
-  const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
-  const host = window.location.host;
-  return new WebSocket(`${protocol}//${host}/api/ws/${sessionId}`);
+  // Tauri 应用直接连接后端
+  return new WebSocket(`ws://localhost:3000/api/ws/${sessionId}`);
 }
 
 // Files