feat: Discord/Slack/ntfy/Matrix targets, command templates, delete protection, email/matrix bots

- Discord, Slack, ntfy, Matrix notification target types with clients and dispatch
- MatrixBot model + API + frontend in Bots tab
- Command template system fully wired into all handler commands
- Default command templates seeded (EN/RU, 14 slots each)
- Command template editor with variables reference including child fields
- Delete protection on all 10 entity types (409 with consumer details)
- Provider type selector on template config forms
- Target type selector as dropdown with all 7 types
- Response template selector on command config form
- CLAUDE.md: mandatory server restart rule, child properties rule

packages/server/src/notify_bridge_server/api/notification_trackers.py

@@ -111,7 +111,9 @@ async def delete_notification_tracker(
     user: User = Depends(get_current_user),
     session: AsyncSession = Depends(get_session),
 ):
+    from .delete_protection import check_notification_tracker, raise_if_used
     tracker = await _get_user_tracker(session, tracker_id, user.id)
+    raise_if_used(await check_notification_tracker(session, tracker.id), tracker.name)
     # Delete associated tracker-target links
     result = await session.exec(
         select(NotificationTrackerTarget).where(NotificationTrackerTarget.tracker_id == tracker_id)