refactor: provider descriptor registry — eliminate provider-specific hardcoding

Replace all if/else chains keyed on provider type strings with a
descriptor-driven architecture. Each provider type (immich, gitea,
planka, scheduler, nut, google_photos) has a descriptor in
frontend/src/lib/providers/ that declares config fields, event
tracking fields, collection metadata, validation, and hooks.

Components now use getDescriptor(type) and render dynamically.
Dashboard provider card shows provider name + type when global
filter is active. Grid-items derived from registry.

frontend/src/lib/i18n/en.json

@@ -186,6 +186,7 @@
 		"repos_count": "repo(s)",
 		"boards_count": "board(s)",
 		"devices_count": "device(s)",
+		"collections_count": "collection(s)",
 		"every": "every",
 		"trackImages": "Track images",
 		"trackVideos": "Track videos",
@@ -403,6 +404,7 @@
 		"name": "Name",
 		"namePlaceholder": "Default tracking",
 		"noConfigs": "No tracking configs yet.",
+		"unknownProviderType": "Unknown provider type",
 		"eventTracking": "Event Tracking",
 		"assetsAdded": "Assets added",
 		"assetsRemoved": "Assets removed",