Web Push notifications

[Wikid82]

Why

Modern browsers (iOS 16.4+ Safari, Android Chrome) support Web Push for installed PWAs, giving native-feeling notifications with no app store and no wrapper. This covers the PWA half of the notification research.

Proposed approach

• Request push permission after install, store subscription server-side per profile
• Send push for relevant events: chore assigned/overdue, reward redemption pending approval (Reward store: approval flow + richer reward types #37)
• No background job infra — notifications are triggered synchronously from the action that causes them (e.g. sending a push at chore-creation time), consistent with the no-background-jobs constraint

Depends on

#32 (PWA foundation).

Acceptance criteria

• A subscribed user receives a push notification for at least one real event (e.g. chore assigned to them)
• Works on both iOS (installed PWA) and Android