feat: NUT (Network UPS Tools) service provider + provider-agnostic UI

Add full NUT support as a polling-based service provider:
- Async TCP client for upsd protocol (port 3493, configurable)
- 8 event types: online, on_battery, low_battery, battery_restored,
  comms_lost, comms_restored, replace_battery, overload
- 3 bot commands: /status, /devices, /battery
- 38 Jinja2 templates (EN+RU notification + command templates)
- Database: tracking config fields, migration, seeds
- Frontend: provider form with host/port/credentials, grid items, i18n

Provider-agnostic UI improvements:
- Remove hardcoded 'immich' defaults from all config forms
- Dynamic collection labels per provider type (Albums/Repos/Boards/UPS Devices)
- Capability-driven test types instead of provider type checks
- Template variable helpers for all providers (was Immich-only)
- Guard Immich-only shared link check to Immich providers
- Auto-clear stale global provider filter from localStorage
- EntitySelect search placeholder shows current selection
- Fix noneLabel in linked target config selectors

New CLAUDE.md rule #8: no provider-specific hardcoding

packages/server/src/notify_bridge_server/services/watcher.py

@@ -123,6 +123,16 @@ async def check_tracker(tracker_id: int) -> dict[str, Any]:
             custom_variables=custom_vars,
         )
         events, new_state = await sched.poll(collection_ids, state_dict)
+    elif provider_type == "nut":
+        from notify_bridge_core.providers.nut import NutServiceProvider
+        nut = NutServiceProvider(
+            host=provider_config.get("host", "localhost"),
+            port=provider_config.get("port", 3493),
+            username=provider_config.get("username"),
+            password=provider_config.get("password"),
+            name=provider_name,
+        )
+        events, new_state = await nut.poll(collection_ids, state_dict)
     else:
         return {"status": "error", "reason": f"unsupported provider type: {provider_type}"}