fix(ui): resolve avatar URL from MinIO; fall back to OAuth provider URL

Add resolveAvatarUrl(userId, storedValue) helper that tries MinIO first,
then falls back to the stored HTTP URL for OAuth users (Google/GitHub)
who have never uploaded a custom avatar.

Add getUserById() to pocketbase helpers for batch avatar resolution in
comments. Update all 6 call sites to use the new helper.

ui/src/routes/profile/+page.server.ts

@@ -1,7 +1,7 @@
 import { fail, redirect } from '@sveltejs/kit';
 import type { Actions, PageServerLoad } from './$types';
 import { changePassword, listUserSessions, getUserByUsername } from '$lib/server/pocketbase';
-import { presignAvatarUrl } from '$lib/server/minio';
+import { resolveAvatarUrl } from '$lib/server/minio';
 import { log } from '$lib/server/logger';
 
 export const load: PageServerLoad = async ({ locals }) => {
@@ -16,13 +16,11 @@ export const load: PageServerLoad = async ({ locals }) => {
 		log.warn('profile', 'listUserSessions failed (non-fatal)', { err: String(e) });
 	}
 
-	// Fetch avatar presigned URL if user has one
+	// Fetch avatar — MinIO first, fall back to OAuth provider picture
 	let avatarUrl: string | null = null;
 	try {
 		const record = await getUserByUsername(locals.user.username);
-		if (record?.avatar_url) {
-			avatarUrl = await presignAvatarUrl(locals.user.id);
-		}
+		avatarUrl = await resolveAvatarUrl(locals.user.id, record?.avatar_url);
 	} catch (e) {
 		log.warn('profile', 'avatar fetch failed (non-fatal)', { err: String(e) });
 	}