feat: colored count badge on Colors sidebar entry

Adds a `colored` field to /library/stats counting non-discarded
photos with a color_label set, mirroring how `rated` is exposed.
The Colors sidebar entry now shows the live count and refreshes
through the existing LIBRARY_STATS_QUERY_KEY invalidations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/LeftSidebar.tsx

@@ -348,7 +348,7 @@ export function LeftSidebar({ onCollapse, onOpenSettings }: LeftSidebarProps) {
         { id: 'all-photos', label: 'All Photos', icon: <Image className="h-4 w-4" />, count: stats?.all_photos ?? 0 },
         { id: 'rated', label: 'Rated', icon: <Star className="h-4 w-4" />, count: stats?.rated ?? 0 },
         { id: 'tags', label: 'Tags', icon: <TagIcon className="h-4 w-4" />, count: tagsTotalCount },
-        { id: 'colors', label: 'Colors', icon: <Palette className="h-4 w-4" /> },
+        { id: 'colors', label: 'Colors', icon: <Palette className="h-4 w-4" />, count: stats?.colored ?? 0 },
         { id: 'duplicates', label: 'Duplicates', icon: <Copy className="h-4 w-4" />, count: stats?.duplicates ?? 0 },
         { id: 'discarded', label: 'Discarded', icon: <Trash2 className="h-4 w-4" />, count: stats?.discarded ?? 0 },
       ],

frontend/src/services/api.ts

@@ -409,6 +409,7 @@ export interface DuplicateGroupsResponse {
 export interface LibraryStats {
   all_photos: number
   rated: number
+  colored: number
   duplicates: number
   discarded: number
   total_photos: number