Issue #41: Model updates for Phase 2 features
Bounty model:
- Add deleted_at: int | None - timestamp when deleted (soft-delete)
- Add created_by_username: str | None - username for display purposes
RoomData model:
- Add timezone: str | None - room's timezone (e.g., "Asia/Jakarta")
- Add admin_user_ids: list[int] - list of admin user IDs
Storage adapter updated to handle new fields in load/save operations.
Tests added for new fields.
