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

.claude/docs/frontend-architecture.md

@@ -43,6 +43,14 @@ Shared entities use a `$state`-based cache layer in `frontend/src/lib/stores/`:
 3. Add `fooCache.clear()` to `clearAllCaches()`
 4. In page components: replace `let foo = $state<Foo[]>([])` with `let foo = $derived(fooCache.items)` and replace `api('/foo')` with `fooCache.fetch()`
 
+## Provider-Aware UI
+
+**IMPORTANT**: UI labels for collections, template variables, and icons MUST be dynamic per provider type — never hardcode Immich-specific terms like "Albums" or `mdiImageMultiple` where other providers will appear.
+
+- **TrackerForm** (`TrackerForm.svelte`): Uses `collectionMeta` lookup by `providerType` for collection label, icon, placeholder, and description.
+- **Template variables** (`/api/template-configs/variables`): Must return variable definitions for ALL provider types (Immich, Gitea, Planka, NUT, Scheduler), not just Immich. When adding a new provider, add its slot variables to `_<provider>_variables()` in `template_configs.py`.
+- **Grid items** (`grid-items.ts`): New provider types must be added to BOTH `providerTypeItems` AND `providerTypeFilterItems`.
+
 ## UI Conventions
 
 ### Selector Placeholders