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/lib/grid-items.ts

@@ -12,6 +12,7 @@ const PROVIDER_TYPE_ICONS: Record<string, string> = {
 	gitea: 'mdiGit',
 	planka: 'mdiViewDashboard',
 	scheduler: 'mdiClockOutline',
+	nut: 'mdiBatteryCharging80',
 };
 
 /** Get the default icon for a provider, falling back by type then generic. */
@@ -118,6 +119,7 @@ export const providerTypeFilterItems = (): GridItem[] => [
 	{ value: 'gitea', icon: 'mdiGit', label: t('providers.typeGitea'), desc: t('gridDesc.providerGitea') },
 	{ value: 'planka', icon: 'mdiViewDashboard', label: t('providers.typePlanka'), desc: t('gridDesc.providerPlanka') },
 	{ value: 'scheduler', icon: 'mdiClockOutline', label: t('providers.typeScheduler'), desc: t('gridDesc.providerScheduler') },
+	{ value: 'nut', icon: PROVIDER_TYPE_ICONS.nut, label: t('providers.typeNut'), desc: t('gridDesc.providerNut') },
 ];
 
 // --- Provider type ---
@@ -127,4 +129,5 @@ export const providerTypeItems = (): GridItem[] => [
 	{ value: 'gitea', icon: PROVIDER_TYPE_ICONS.gitea, label: t('providers.typeGitea'), desc: t('gridDesc.providerGitea') },
 	{ value: 'planka', icon: PROVIDER_TYPE_ICONS.planka, label: t('providers.typePlanka'), desc: t('gridDesc.providerPlanka') },
 	{ value: 'scheduler', icon: PROVIDER_TYPE_ICONS.scheduler, label: t('providers.typeScheduler'), desc: t('gridDesc.providerScheduler') },
+	{ value: 'nut', icon: PROVIDER_TYPE_ICONS.nut, label: t('providers.typeNut'), desc: t('gridDesc.providerNut') },
 ];