feat: bulk rating / color / discard / pick from selection

Culling actions used to operate on a single photo (the activePhotoId)
even when many were selected — pressing 5 with ten thumbnails high-
lighted only rated one. Same for the RightSidebar buttons, which
weren't even visible in multi-select mode. Lightroom semantics: every
culling action applies to the whole selection.

Fix
- Three new bulk helpers in services/api.ts:
    photos.bulkSetRating(ids, rating)
    photos.bulkSetColor(ids, color | null)
    (existing photos.bulkDiscard / bulkRestore reused for X / U)
  All matching the backend BulkAction { ids, action, value } shape
  the /photos/bulk endpoint already accepts.

useKeyboardShortcuts
- New cullTargets() helper: selectedPhotos if non-empty, else
  activePhotoId in a singleton, else empty.
- updateActive() now branches on cullTargets().length:
    1 → existing PATCH /photos/{id} path (single-photo).
    2+ → fans out to the right bulk endpoint per field. rating goes
         to bulkSetRating, color_label to bulkSetColor, is_discarded
         to bulkDiscard / bulkRestore.
- 1-5 / 0 / X / U / 6-9 shortcuts now Just Work on multi-select
  without further changes — they all funnel through updateActive.

RightSidebar
- Restructured the Quick Actions block: filename / title / notes are
  hidden in multi-select (they only make sense for one photo); but
  rating / color / flag controls are now always visible when at
  least one photo is selected. A small "Rating, color, and flag
  apply to all N selected" hint shows in multi mode.
- New applyRating / setColor / applyDiscard helpers fan out to the
  bulk endpoints when selectedPhotos.length > 1, otherwise hit the
  per-photo PATCH path. The displayed value still reflects the
  active photo (last clicked) so the user has a visual anchor —
  matches Lightroom's "focused vs selected" model.
- Pick/Heap-toggle button is now selection-aware too: heapMutation
  takes ids[], the click handler reads selectedPhotos, and the
  add-vs-remove decision uses "every selected is a member" exactly
  like the P keyboard shortcut. Optimistic membership cache update
  also flips the basket badge across all selected thumbnails
  instantly.

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

frontend/src/hooks/useKeyboardShortcuts.ts

@@ -55,10 +55,74 @@ export function useKeyboardShortcuts(props: KeyboardShortcutsProps) {
     },
   })
 
+  const invalidatePhotoQueries = () => {
+    queryClient.invalidateQueries({ queryKey: ['photo'] })
+    queryClient.invalidateQueries({ queryKey: ['photos'] })
+  }
+
+  const bulkRatingMutation = useMutation({
+    mutationFn: ({ ids, rating }: { ids: string[]; rating: number }) =>
+      photosApi.bulkSetRating(ids, rating),
+    onSuccess: invalidatePhotoQueries,
+    onError: (e: any) => toast.error('Bulk rating failed', e.message || 'Unknown error'),
+  })
+
+  const bulkColorMutation = useMutation({
+    mutationFn: ({ ids, color }: { ids: string[]; color: string | null }) =>
+      photosApi.bulkSetColor(ids, color),
+    onSuccess: invalidatePhotoQueries,
+    onError: (e: any) => toast.error('Bulk color failed', e.message || 'Unknown error'),
+  })
+
+  const bulkDiscardMutation = useMutation({
+    mutationFn: (ids: string[]) => photosApi.bulkDiscard(ids),
+    onSuccess: invalidatePhotoQueries,
+    onError: (e: any) => toast.error('Bulk discard failed', e.message || 'Unknown error'),
+  })
+
+  const bulkRestoreMutation = useMutation({
+    mutationFn: (ids: string[]) => photosApi.bulkRestore(ids),
+    onSuccess: invalidatePhotoQueries,
+    onError: (e: any) => toast.error('Bulk restore failed', e.message || 'Unknown error'),
+  })
+
+  /** The set of photo ids the next culling action should apply to.
+   *  - Multi-selection → all selected photos
+   *  - Single selection → that one photo
+   *  - No selection but an activePhotoId set (last clicked) → that one
+   *  - Otherwise → empty
+   */
+  const cullTargets = (): string[] => {
+    const state = usePhotoStore.getState()
+    if (state.selectedPhotos.length > 0) return state.selectedPhotos
+    if (state.activePhotoId) return [state.activePhotoId]
+    return []
+  }
+
+  /** Apply a partial PhotoUpdate to the cull targets. Picks the right
+   *  bulk endpoint when there are 2+ photos so a single API call covers
+   *  the whole selection. */
   const updateActive = (data: PhotoUpdate) => {
-    const id = usePhotoStore.getState().activePhotoId
-    if (!id) return
-    updateMutation.mutate({ id, data })
+    const ids = cullTargets()
+    if (ids.length === 0) return
+
+    if (ids.length === 1) {
+      updateMutation.mutate({ id: ids[0], data })
+      return
+    }
+
+    // Multi-selection — fan out to the right bulk endpoint per field.
+    if (data.rating !== undefined) {
+      bulkRatingMutation.mutate({ ids, rating: data.rating })
+    }
+    if (data.color_label !== undefined) {
+      bulkColorMutation.mutate({ ids, color: data.color_label })
+    }
+    if (data.is_discarded === true) {
+      bulkDiscardMutation.mutate(ids)
+    } else if (data.is_discarded === false) {
+      bulkRestoreMutation.mutate(ids)
+    }
   }
 
   // P key (Pick): toggle the current selection's membership in the active