feat(frontend): fullscreen toggle and album back button

- add fullscreen/fullscreen_exit icons and a top-bar toggle (right of themes)
- add back arrow left of the album title to return to the albums overview

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

@@ -155,7 +155,17 @@
 		<div
 			class="border-border bg-chrome sticky top-0 z-10 flex items-center justify-between gap-3 border-b px-3 py-2"
 		>
-			<h1 class="text-text truncate text-sm font-medium">{album?.title ?? ''}</h1>
+			<div class="flex min-w-0 items-center gap-1">
+				<a
+					href="/"
+					class="text-text-muted hover:bg-bg-muted hover:text-text inline-flex shrink-0 items-center justify-center rounded-md p-1.5"
+					aria-label="Ко всем альбомам"
+					title="Ко всем альбомам"
+				>
+					<Icon name="arrow_back" class="size-5" />
+				</a>
+				<h1 class="text-text truncate text-sm font-medium">{album?.title ?? ''}</h1>
+			</div>
 			<div class="flex items-center gap-3">
 				<DensityControl />
 				{#if canUpload}