feat: add Scheduler provider + multi-provider UX fixes

Scheduler provider:
- Virtual provider (no external service) that emits SCHEDULED_MESSAGE
  events on user-defined intervals or cron expressions
- Custom variables stored in tracker filters, flattened into template context
- fire_count persists across triggers via tracker state
- APScheduler CronTrigger support for cron-mode schedules
- Default templates (EN+RU), seeded on startup

Multi-provider UX fixes:
- Tracking config hides Immich-specific sections (periodic, scheduled,
  memory, asset display) for non-Immich providers
- Command config driven by provider capabilities — hides commands/settings
  for providers without bot commands
- Template config hides empty "Scheduled Messages" group
- Test menu on tracker targets is provider-aware (Immich shows all 4 test
  types, others show only basic)
- Removed redundant Test button from tracker card
- System-owned tracking configs (user_id=0) seeded for Gitea + Scheduler
- Fixed ownership checks to allow system configs in tracker-target links
- Capabilities cache shared across template-configs and command-configs
- Command tracker bot selector uses EntitySelect instead of raw select
- Sample context includes Gitea + Scheduler variables for template preview

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

@@ -101,7 +101,10 @@ async def list_configs(
     user: User = Depends(get_current_user),
     session: AsyncSession = Depends(get_session),
 ):
-    query = select(TrackingConfig).where(TrackingConfig.user_id == user.id)
+    from sqlmodel import or_
+    query = select(TrackingConfig).where(
+        or_(TrackingConfig.user_id == user.id, TrackingConfig.user_id == 0)
+    )
     if provider_type:
         query = query.where(TrackingConfig.provider_type == provider_type)
     result = await session.exec(query)
@@ -167,6 +170,6 @@ def _response(c: TrackingConfig) -> dict:
 
 async def _get(session: AsyncSession, config_id: int, user_id: int) -> TrackingConfig:
     config = await session.get(TrackingConfig, config_id)
-    if not config or config.user_id != user_id:
+    if not config or (config.user_id != user_id and config.user_id != 0):
         raise HTTPException(status_code=404, detail="Tracking config not found")
     return config