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/PhotoGrid.svelte

@@ -13,6 +13,7 @@
 	helpers.
 -->
 <script lang="ts">
+	import { untrack } from 'svelte';
 	import {
 		isSelected,
 		selection,
@@ -40,6 +41,26 @@
 	const order = $derived(photos.map((p) => p.UID));
 	$effect(() => {
 		setOrder(order);
+		// Re-anchor focus when the previously focused photo isn't part of
+		// this grid — covers drilling into a /tags category from any
+		// other view, where the selection.focused module state would
+		// otherwise leak across surfaces and the new grid would render
+		// with no tile highlighted. Crucially we only re-anchor when the
+		// uid is *absent*, so refetches that keep the focused photo
+		// around (e.g. after `focusAfter` set the next photo on archive)
+		// don't snap focus back to photos[0].
+		untrack(() => {
+			if (order.length === 0) {
+				setFocused(null);
+				selection.ids.clear();
+				return;
+			}
+			const cur = selection.focused;
+			if (cur && order.includes(cur)) return;
+			setFocused(order[0]);
+			setAnchor(order[0]);
+			selection.ids.clear();
+		});
 	});
 
 	function onClick(e: MouseEvent, uid: string) {