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/sidebar/BulkMetadataSidebar.svelte

@@ -119,10 +119,10 @@
 	}
 
 	const COLOR_SWATCHES: { key: string; bg: string; title: string }[] = [
-		{ key: 'red', bg: 'bg-red-500', title: 'Red' },
-		{ key: 'orange', bg: 'bg-orange-500', title: 'Orange' },
-		{ key: 'yellow', bg: 'bg-yellow-400', title: 'Yellow' },
-		{ key: 'green', bg: 'bg-green-500', title: 'Green' }
+		{ key: 'red', bg: 'bg-red-500', title: 'Red — reject' },
+		{ key: 'orange', bg: 'bg-orange-500', title: 'Orange — review' },
+		{ key: 'yellow', bg: 'bg-yellow-400', title: 'Yellow — pick' },
+		{ key: 'green', bg: 'bg-green-500', title: 'Green — keep' }
 	];
 
 	async function applyKeyword() {