feat(profile): add round avatar with upload and cropping

- backend: user_avatar_objects binding (PG+SQLite), GC preserves avatar blobs,
  avatar service (EXIF-stripping WebP 128/512), public avatar read route
- web: avatar upload/crop on profile, round avatar in header/members/comments/author
- android: avatar upload/crop, round avatar on profile and albums header
- openspec: add-user-avatar proposal/design/specs/tasks

frontend/src/lib/components/AppShell.svelte

@@ -2,6 +2,7 @@
 	import { onMount } from 'svelte';
 	import { goto } from '$app/navigation';
 	import { authApi } from '$lib/api';
+	import Avatar from './Avatar.svelte';
 	import Emblem from './Emblem.svelte';
 	import Icon from './Icon.svelte';
 	import ThemeSwitcher from './ThemeSwitcher.svelte';
@@ -135,10 +136,10 @@
 			{#if auth.isAuthenticated}
 				<a
 					href="/profile"
-					class="text-text-muted hover:text-text inline-flex items-center gap-1 text-xs"
+					class="text-text-muted hover:text-text inline-flex items-center gap-1.5 text-xs"
 					title="Профиль"
 				>
-					<Icon name="settings" class="size-4" />
+					<Avatar name={auth.user?.name} url={auth.user?.avatar_url} size="size-6" />
 					<span class="hidden sm:inline">{auth.user?.name ?? 'Профиль'}</span>
 				</a>
 				<button