feat(frontend): collapsible right-panel sections with photo info

- add PanelSection with persisted collapse state
- restructure album and photo panels into sections
- add "Информация" section with EXIF/metadata (size, type, resolution, taken, coords)

frontend/src/lib/components/PanelSection.svelte

@@ -0,0 +1,46 @@
+<script lang="ts">
+	import { onMount } from 'svelte';
+	import Icon from './Icon.svelte';
+	import type { Snippet } from 'svelte';
+
+	interface Props {
+		id: string;
+		title: string;
+		open?: boolean;
+		children: Snippet;
+	}
+
+	let { id, title, open = true, children }: Props = $props();
+
+	// svelte-ignore state_referenced_locally
+	let isOpen = $state(open);
+
+	onMount(() => {
+		const v = localStorage.getItem(`panel-section-${id}`);
+		if (v === '0') isOpen = false;
+		else if (v === '1') isOpen = true;
+	});
+
+	function toggle() {
+		isOpen = !isOpen;
+		localStorage.setItem(`panel-section-${id}`, isOpen ? '1' : '0');
+	}
+</script>
+
+<section class="border-border border-b">
+	<button
+		type="button"
+		class="text-text-muted hover:text-text flex w-full items-center justify-between gap-2 px-4 py-2.5 text-left"
+		aria-expanded={isOpen}
+		onclick={toggle}
+	>
+		<span class="text-xs font-semibold tracking-wide uppercase">{title}</span>
+		<Icon
+			name="expand_more"
+			class="size-4 shrink-0 transition-transform {isOpen ? 'rotate-180' : ''}"
+		/>
+	</button>
+	{#if isOpen}
+		<div class="px-4 pb-4">{@render children()}</div>
+	{/if}
+</section>