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/Comments.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { api } from '$lib/api';
+	import Avatar from './Avatar.svelte';
 	import Icon from './Icon.svelte';
 	import { auth } from '$lib/stores/auth.svelte';
 	import type { Comment } from '$lib/types';
@@ -56,8 +57,9 @@
 <div class="mt-2">
 	{#each comments as comment (comment.id)}
 		<div class="border-border mb-1 flex items-start justify-between gap-2 border-b py-1 text-sm">
-			<span class="text-text">
-				<strong>{comment.user.name}</strong>: {comment.text}
+			<span class="text-text inline-flex items-start gap-2">
+				<Avatar name={comment.user.name} url={comment.user.avatar_url} size="size-6" />
+				<span><strong>{comment.user.name}</strong>: {comment.text}</span>
 			</span>
 			{#if auth.user?.id === comment.user_id}
 				<button