Add editable recovery calendar dates and fix notification persistence on friend request actions

[Copilot]

The recovery calendar was read-only, and friend request accept/decline actions removed notifications entirely instead of marking them as read.

Calendar date editing

• Added updateCalendarDay(userId, date, markAsRelapse, triggers?, notes?) to firebase.ts — rewrites the user's relapses array for the target date (remove existing entry, optionally insert new one)
• Added editable?: boolean prop to RelapseCalendar; when true, days are clickable and open a dialog to toggle clean/relapse with trigger + notes fields
• Analytics.tsx passes editable={true} since it always renders the current user's own calendar

<RelapseCalendar userId={currentUser?.uid} editable={true} />

Notification read behavior

• Accepting or declining a friend request now calls markNotificationAsRead() and updates local state (read: true) instead of pushing the ID into a dismissedIds set
• Read friend-request notifications render dimmed (opacity-60) with accept/decline buttons hidden — consistent with standard app notification UX
• Removed the now-unused dismissedIds state

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.