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/providers.py

@@ -189,7 +189,9 @@ async def delete_provider(
     session: AsyncSession = Depends(get_session),
 ):
     """Delete a service provider."""
+    from .delete_protection import check_service_provider, raise_if_used
     provider = await _get_user_provider(session, provider_id, user.id)
+    raise_if_used(await check_service_provider(session, provider.id), provider.name)
     await session.delete(provider)
     await session.commit()