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/components/timeline/BulkActionBar.svelte

@@ -14,7 +14,12 @@
 		type PpAlbum
 	} from '$lib/services/photoprism';
 	import { batchEdit } from '$lib/services/batch';
-	import { clearSelection, selection, setFocused } from '$lib/stores/selection.svelte';
+	import {
+		clearSelection,
+		focusAfter,
+		selection,
+		setFocused
+	} from '$lib/stores/selection.svelte';
 	import { filters } from '$lib/stores/filters.svelte';
 	import { popAndRun, push as pushUndo, undoStack } from '$lib/stores/undo.svelte';
 	import { isAuthenticated } from '$lib/stores/session.svelte';
@@ -98,6 +103,10 @@
 					await batchRestore(ids);
 					void qc.invalidateQueries({ queryKey: ['photos'] });
 				});
+				// Advance focus to the photo immediately after the archived
+				// set before the multi-selection is dropped — lets the user
+				// keep stepping through the timeline with X.
+				focusAfter(ids);
 				clearSelection();
 				toast.success(`Archived ${ids.length}`);
 			} catch (err) {
@@ -173,11 +182,27 @@
 		heapPickerOpen = false;
 		await withBusy(async () => {
 			try {
-				await addToHeap(heap.UID, ids);
+				const { added } = await addToHeap(heap.UID, ids);
 				qc.invalidateQueries({ queryKey: ['heaps'] });
-				toast.success(`Added ${ids.length} → ${heap.Title}`);
-				pushUndo(`Added ${ids.length} to ${heap.Title}`, async () => {
-					await removeFromHeap(heap.UID, ids);
+				// PhotoPrism returns 200 even when nothing was added (UIDs
+				// already present or unknown to the index) — surface the
+				// real delta so the user isn't fooled by a green toast over
+				// a no-op.
+				if (added.length === 0) {
+					toast.error(`Nothing added to ${heap.Title}`, {
+						description: `PhotoPrism rejected all ${ids.length} UIDs (already in heap, or not indexed).`
+					});
+					return;
+				}
+				if (added.length < ids.length) {
+					toast.success(`Added ${added.length}/${ids.length} → ${heap.Title}`, {
+						description: 'The rest were already in this heap.'
+					});
+				} else {
+					toast.success(`Added ${added.length} → ${heap.Title}`);
+				}
+				pushUndo(`Added ${added.length} to ${heap.Title}`, async () => {
+					await removeFromHeap(heap.UID, added);
 					qc.invalidateQueries({ queryKey: ['heaps'] });
 				});
 				clearSelection();