feat(timeline): focus follows archive, snaps to first on view load

- New selection.focusAfter(excluded) walks selection.order forward past
  the archived/restored set so X-ing through the timeline keeps the
  cursor on the next live photo instead of falling back to photo[0]
  via the auto-anchor effect. Wired into gridKeyNav.toggleArchive (X
  key) and BulkActionBar.onArchive.
- Auto-focus effect on the timeline always re-anchors to photos[0] on
  view load (pageCount → 1), instead of preserving a stale uid from
  the previous filter.
- PhotoGrid re-anchors focus when the previously focused uid isn't in
  the new photo set, so drilling into a /tags category drops the
  cursor on its first tile instead of carrying a stale selection from
  whatever view the user came from.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/services/photoprism.ts

@@ -500,8 +500,19 @@ export async function deleteHeap(uid: string): Promise<void> {
 	await http.delete(`/albums/${uid}`);
 }
 
-export async function addToHeap(uid: string, photos: string[]): Promise<void> {
-	await http.post(`/albums/${uid}/photos`, { photos });
+/**
+ * PhotoPrism returns `{ code, message, album, photos: [uids in album], added: [delta] }`.
+ * Surface `added` so callers can detect "200-but-nothing-happened" — PhotoPrism
+ * silently skips UIDs that are missing from the index or already in the album,
+ * which used to look like a successful add to the user.
+ */
+export interface AddToHeapResult {
+	added: string[];
+}
+
+export async function addToHeap(uid: string, photos: string[]): Promise<AddToHeapResult> {
+	const { data } = await http.post<{ added?: string[] }>(`/albums/${uid}/photos`, { photos });
+	return { added: data.added ?? [] };
 }
 
 export async function removeFromHeap(uid: string, photos: string[]): Promise<void> {