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/i18n/en.json

@@ -111,6 +111,7 @@
 		"typeGitea": "Gitea",
 		"typePlanka": "Planka",
 		"typeScheduler": "Scheduler",
+		"typeNut": "NUT (UPS)",
 		"loadError": "Failed to load providers.",
 		"externalDomain": "External Domain",
 		"optional": "optional",
@@ -127,6 +128,13 @@
 		"apiTokenHint": "Optional. Needed for connection testing and repository listing.",
 		"webhookUrl": "Webhook URL",
 		"webhookUrlHint": "Set this as the Target URL in Gitea webhook settings (relative to your bridge host).",
+		"nutHost": "NUT Server Host",
+		"nutHostPlaceholder": "192.168.1.100 or ups.local",
+		"nutPort": "NUT Server Port",
+		"nutUsername": "Username",
+		"nutPassword": "Password",
+		"nutUsernameHint": "Optional — only needed if upsd requires authentication",
+		"nutPasswordHint": "Optional — upsd user password",
 		"testAndSave": "Test & Save",
 		"saveWithoutTest": "Save without testing"
 	},
@@ -141,6 +149,12 @@
 		"selectServer": "Select provider...",
 		"albums": "Albums",
 		"selectAlbums": "Select albums...",
+		"repositories": "Repositories",
+		"selectRepositories": "Select repositories...",
+		"boards": "Boards",
+		"selectBoards": "Select boards...",
+		"upsDevices": "UPS Devices",
+		"selectUpsDevices": "Select UPS devices...",
 		"eventTypes": "Event Types",
 		"notificationTargets": "Notification Targets",
 		"scanInterval": "Scan Interval (seconds)",
@@ -826,7 +840,8 @@
 		"providerImmich": "Self-hosted photo server",
 		"providerGitea": "Self-hosted Git service",
 		"providerPlanka": "Self-hosted Kanban board",
-		"providerScheduler": "Time-based scheduled messages"
+		"providerScheduler": "Time-based scheduled messages",
+		"providerNut": "Network UPS monitoring"
 	},
 	"error": {
 		"notFound": "Page not found",