F14: Push notifications — reminders on iOS and Android

## What to build

Implement push notifications so users are reminded about due chores. Notifications should be configurable per chore: at due time, on a repeating interval, or after an overdue threshold. Requires platform support on iOS and Android.

This is a feasibility and architecture slice: establish the notification infrastructure, permission flows, and at least one working notification type end-to-end.

## Acceptance criteria

- [ ] User can grant/deny notification permission from within the app
- [ ] At least one notification trigger works end-to-end (e.g. "notify at due time")
- [ ] Per-chore notification settings (on/off, trigger type) are configurable
- [ ] Notifications deep-link back to the relevant chore on tap
- [ ] Tested on both iOS and Android
- [ ] Notification payload respects user's chosen reminder mode (due time / interval / overdue)

## Blocked by

None — can start immediately

此 issue 描述了一個適用於 React Native 應用程式的跨平台推播通知系統。先探索 repository 中現有的通知處理與權限流程。尋找如 react-native-push-notification 或 Expo 的通知模組等函式庫。驗收標準列出了需要實作的主要功能：權限流程、可設定的觸發器、deep linking，以及在 iOS 和 Android 上進行測試。「完成」表示至少有一個通知觸發器能夠端到端運作，且設定可依每個 chore 進行設定。

由索引模型根據 Issue 內容生成。