fix: 超时设置0值(禁用)无法保存的bug

- 保存值改用-1表示默认, 0表示禁用, 正数表示自定义秒数
- 修复parseSec区分空字符串和0值
- loadTimeoutSettings/main.ts初始化同步更新判断逻辑
- 补全types.d.ts中setTimeouts类型声明

src/renderer/types.d.ts

@@ -220,6 +220,7 @@ export interface MetonaDesktopAPI {
     execute: (toolName: string, args: Record<string, unknown>) => Promise<ToolResult>;
     getConfig: () => Promise<{ allowedDirs: string[]; blockedDirs: string[] }>;
     setAllowedDirs: (dirs: string[]) => Promise<void>;
+    setTimeouts: (timeouts: { http?: number; mcp?: number }) => Promise<{ success: boolean }>;
   };
   notify: (title: string, body: string) => void;
   window: {