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

frontend/src/routes/+layout.svelte

@@ -42,6 +42,14 @@
 		globalProviderFilter.set(v === 0 ? null : v);
 	});
 
+	// Sync store → filter value (handles auto-clear of stale IDs)
+	$effect(() => {
+		const storeId = globalProviderFilter.id;
+		if (storeId === null && providerFilterValue !== 0) {
+			providerFilterValue = 0;
+		}
+	});
+
 	let showPasswordForm = $state(false);
 	let redirecting = $state(false);
 	let openSearch: (() => void) | undefined;