fix: avoid Tauri window access in browser mode

[squarepots]

本 PR 修复 plain browser/LAN 模式在 React mount 前访问 Tauri window API 导致的空白页。所有原生窗口操作现在都通过 lazy runtime boundary：只有检测到 window.__TAURI_INTERNALS__ 后才解析并缓存 Tauri window。

drag、双击 maximize、resize listener、minimize、maximize 和 close 都使用该 helper；浏览器模式不渲染原生窗口控件，Tauri desktop 保留现有窗口交互。

验证

• pnpm test:browser-runtime：2 项通过，覆盖无 window 和 plain browser-like window
• pnpm test:desktop-reopen：7 项通过
• pnpm test:close-preference：3 项通过
• pnpm test:reset-credits：3 项通过
• pnpm build：通过

Closes #145

---

This PR fixes the blank page in plain browser/LAN mode caused by accessing the Tauri window API before React mounts. Native window operations now go through a lazy runtime boundary that resolves and caches the Tauri window only when window.__TAURI_INTERNALS__ is present.

Dragging, double-click maximize, resize listeners, minimize, maximize, and close all use the helper. Browser mode does not render native window controls, while the Tauri desktop keeps its existing window interactions.

Validation

• pnpm test:browser-runtime: 2 passed, covering no window and a plain browser-like window
• pnpm test:desktop-reopen: 7 passed
• pnpm test:close-preference: 3 passed
• pnpm test:reset-credits: 3 passed
• pnpm build: passed

Closes #145