feat: lightroom-style workspace UI with album covers

Backend:
- expose cover thumbnail URL on album responses (LEFT JOIN + presign)
- auto-assign cover only when empty; FK cover_photo_id -> photos ON DELETE SET NULL
- add photos_count / members_count to album responses; cover repo test

Frontend:
- split layouts into (app) shell (resizable rail + contextual panel) and (public)
- album rail + create-album dialog; album panel with cover picker / make-cover
- photo viewer route with filmstrip, replacing lightbox; share reuses it
- grid density slider, toolbar + drag-and-drop upload, dark graphite default

OpenSpec: add lightroom-workspace-ui change (proposal, design, specs, tasks)

frontend/src/routes/+layout.svelte

@@ -1,18 +1,17 @@
 <script lang="ts">
 	import { onMount } from 'svelte';
-	import { goto } from '$app/navigation';
 	import '../app.css';
-	import ThemeSwitcher from '$lib/components/ThemeSwitcher.svelte';
-	import Icon from '$lib/components/Icon.svelte';
 	import IconSprite from '$lib/components/IconSprite.svelte';
 	import { auth } from '$lib/stores/auth.svelte';
 	import { theme } from '$lib/stores/theme.svelte';
+	import { density } from '$lib/stores/density.svelte';
 	import { authApi } from '$lib/api';
 
 	let { children } = $props();
 
 	onMount(() => {
 		theme.init();
+		density.init();
 		if (auth.isAuthenticated && !auth.user) {
 			authApi
 				.me()
@@ -20,49 +19,7 @@
 				.catch(() => {});
 		}
 	});
-
-	async function logout() {
-		if (auth.refresh) {
-			await authApi.logout(auth.refresh).catch(() => {});
-		}
-		auth.clear();
-		goto('/login');
-	}
 </script>
 
 <IconSprite />
-<div class="bg-bg text-text min-h-screen">
-	<header class="border-border bg-bg-elevated border-b">
-		<div class="mx-auto flex max-w-6xl items-center justify-between gap-4 px-4 py-3">
-			<a href="/" class="inline-flex items-center gap-2 text-lg font-semibold">
-				<Icon name="photo_camera" />
-				Galo
-			</a>
-			<div class="flex items-center gap-3">
-				{#if auth.isAuthenticated}
-					<span class="text-text-muted hidden text-sm sm:inline">{auth.user?.name ?? ''}</span>
-					<button
-						type="button"
-						class="text-text-muted hover:text-text inline-flex items-center gap-1.5 text-sm"
-						onclick={logout}
-					>
-						<Icon name="logout" class="size-4" />
-						Выйти
-					</button>
-				{:else}
-					<a
-						href="/login"
-						class="text-text-muted hover:text-text inline-flex items-center gap-1.5 text-sm"
-					>
-						<Icon name="login" class="size-4" />
-						Войти
-					</a>
-				{/if}
-				<ThemeSwitcher />
-			</div>
-		</div>
-	</header>
-	<main class="mx-auto max-w-6xl px-4 py-6">
-		{@render children()}
-	</main>
-</div>
+{@render children()}