feat(web): keyboard rating/color marks, search focus, shortcuts overlay

Lightroom-style keys in grid+preview: 0-5 rating (re-key toggles),
6-9 color labels, optimistic marks cache patch with rollback. / focuses
the search box, ? opens a new shortcut-reference overlay that inertly
swallows other keys while open.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/src/routes/+layout.svelte

@@ -20,6 +20,7 @@
 	import AnimatedMule from '$lib/components/mule/AnimatedMule.svelte';
 	import PreviewModal from '$lib/components/preview/PreviewModal.svelte';
 	import MoveToFolderDialog from '$lib/components/layout/MoveToFolderDialog.svelte';
+	import ShortcutsDialog from '$lib/components/layout/ShortcutsDialog.svelte';
 
 	let { children } = $props();
 
@@ -122,6 +123,8 @@
 		     store. Opened from the heap/folder kebabs, the BulkActionBar
 		     button, and the `m` shortcut — all through openMove(). -->
 		<MoveToFolderDialog />
+		<!-- Keyboard-shortcut reference, toggled by `?` via gridKeyNav. -->
+		<ShortcutsDialog />
 	{:else}
 		{@render children?.()}
 	{/if}