fix: refresh sidebar counts after photo mutations

LIBRARY_STATS_QUERY_KEY was never invalidated by the bulk/single
mutation paths in RightSidebar and PhotoInfoPanel, so the All Photos
/ Rated / Discarded / Tags badges only updated on reload. Add it to
both shared invalidation helpers and the inline updateMutation, and
correct the stale docstring on useLibraryStatsQuery.

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

frontend/src/hooks/useLibraryStatsQuery.ts

@@ -6,8 +6,9 @@ export const LIBRARY_STATS_QUERY_KEY = ['library', 'stats'] as const
 /**
  * Per-section counts for the LeftSidebar badges (All Photos, Rated,
  * Duplicates, Discarded). Cached briefly so navigating around doesn't
- * re-fetch on every click; invalidated on photo mutations through the
- * standard ['photos'] invalidation in the mutation onSuccess paths.
+ * re-fetch on every click. Mutations that change a photo's rating,
+ * discard flag, tags, etc. must invalidate LIBRARY_STATS_QUERY_KEY in
+ * their onSuccess so the badges stay live.
  */
 export function useLibraryStatsQuery() {
   return useQuery<LibraryStats>({