- Add account deletion with tombstone (isDeleted flag), password/username
confirmation, owned-space guard, and full cleanup transaction
- Free deleted usernames by renaming to !deleted:<id> so they can be reused
- Add migration to retroactively free usernames from already-tombstoned users
- Add GET /api/auth/check-username endpoint with rate limiting for real-time
availability checking during registration
- Add debounced username availability indicator on registration Step 1
- Add DeleteAccountModal with federation-aware remote account cleanup
- Add federation ops utility for remote instance management
- Update sanitizeUser to anonymize deleted user profiles
- Add instance store improvements and connected instances modal updates