Implement Progressive Web App (PWA)

[FerdinandSu]

Description / 描述

English:
Convert an existing frontend implementation (from Issue #25 or #26) into a Progressive Web App with offline support.

Features to implement:

• Service worker for offline caching
• App manifest for installability
• Offline data persistence (IndexedDB)
• Sync data when back online
• Push notifications (optional)
• App-like experience on mobile

Tech Stack:

• vite-plugin-pwa
• Workbox for service worker
• IndexedDB or localForage for storage

中文:
将现有的前端实现（来自 Issue #25 或 #26）转换为具有离线支持的渐进式 Web 应用程序。

Difficulty / 难度

Medium / 中等

Estimated Time / 预计时间

6-8 hours

⚠️ Important Requirements / 重要要求

• Use vite-plugin-pwa
• PR MUST include screenshots of PWA install prompt and offline mode

Acceptance Criteria / 验收标准

• Install and configure vite-plugin-pwa
• Create app manifest
• Implement service worker with caching strategies
• Add offline data persistence
• Implement sync when online
• App is installable on mobile devices
• Lighthouse PWA score >90
• PR MUST include screenshots of PWA install prompt and offline mode

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