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/lib/components/PhotoGrid.svelte

@@ -5,10 +5,12 @@
 
 	interface Props {
 		photos: Photo[];
+		selectedId?: string | null;
+		onSelect?: (index: number) => void;
 		onOpen?: (index: number) => void;
 	}
 
-	let { photos, onOpen }: Props = $props();
+	let { photos, selectedId = null, onSelect, onOpen }: Props = $props();
 </script>
 
 {#if photos.length === 0}
@@ -22,8 +24,13 @@
 			<li>
 				<button
 					type="button"
-					class="border-border bg-bg-muted group relative block aspect-square w-full overflow-hidden rounded-lg border"
-					onclick={() => onOpen?.(i)}
+					class="border-border bg-bg-muted group relative block aspect-square w-full overflow-hidden rounded-lg border {photo.id ===
+					selectedId
+						? 'ring-primary ring-2'
+						: ''}"
+					aria-pressed={photo.id === selectedId}
+					onclick={() => onSelect?.(i)}
+					ondblclick={() => onOpen?.(i)}
 				>
 					{#if photo.thumb_url}
 						<img