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/lib/components/Comments.svelte

@@ -75,18 +75,20 @@
 	{/each}
 
 	{#if auth.isAuthenticated}
-		<form class="mt-2 flex gap-2" onsubmit={submit}>
+		<form class="relative mt-2" onsubmit={submit}>
 			<input
 				bind:value={text}
 				placeholder="Комментарий…"
-				class="border-border bg-bg text-text flex-1 rounded-lg border px-3 py-1.5 text-sm"
+				class="border-border bg-bg text-text w-full rounded-lg border py-1.5 pr-10 pl-3 text-sm"
 			/>
 			<button
-				class="bg-primary text-primary-fg inline-flex items-center gap-1.5 rounded-lg px-3 py-1.5 text-sm"
+				class="text-primary hover:bg-bg-muted absolute top-1/2 right-1 inline-flex -translate-y-1/2 items-center justify-center rounded-md p-1.5 disabled:opacity-50"
 				type="submit"
+				aria-label="Отправить"
+				title="Отправить"
+				disabled={!text.trim()}
 			>
 				<Icon name="send" class="size-4" />
-				Отправить
 			</button>
 		</form>
 	{/if}