feat(frontend): select photo in album grid and show info in panel

- single click selects a photo (ring + aria-pressed) and shows its info in the right panel without navigating; double click opens the viewer
- shared 'selection' store; panel uses the route photo in viewer mode and the selected photo in album mode; selection resets on album change
- openspec: sync lightroom-workspace-ui (grid-selection requirement, viewer chrome wording without timers, nested f fullscreen, tasks 9.9/9.10)

frontend/src/routes/(app)/albums/[id]/+page.svelte

@@ -8,6 +8,7 @@
 	import Icon from '$lib/components/Icon.svelte';
 	import { auth } from '$lib/stores/auth.svelte';
 	import { albums } from '$lib/stores/albums.svelte';
+	import { selection } from '$lib/stores/selection.svelte';
 	import { SSEClient, type SSEEvent } from '$lib/sse';
 	import type { Album, Photo } from '$lib/types';
 
@@ -50,6 +51,7 @@
 
 	$effect(() => {
 		const id = albumId;
+		selection.clear();
 		loading = true;
 		error = '';
 		Promise.all([loadAlbum(), loadPhotos()])
@@ -200,6 +202,11 @@
 			{:else}
 				<PhotoGrid
 					{photos}
+					selectedId={selection.albumId === albumId ? (selection.photo?.id ?? null) : null}
+					onSelect={(i) => {
+						const p = photos[i];
+						if (p) selection.select(albumId, p);
+					}}
 					onOpen={(i) => {
 						const p = photos[i];
 						if (p) goto(`/albums/${albumId}/photos/${p.id}`);