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/lib/server/minio.ts

@@ -40,8 +40,8 @@ export async function presignAvatarUploadUrl(userId: string, mimeType: string):
 }
 
 /**
- * Returns a presigned GET URL for a user's avatar, rewritten to the public URL.
- * Returns null if no avatar exists.
+ * Returns a presigned GET URL for a user's avatar from MinIO.
+ * Returns null if no avatar object exists in MinIO for this user.
  */
 export async function presignAvatarUrl(userId: string): Promise<string | null> {
 	const res = await backendFetch(`/api/presign/avatar/${encodeURIComponent(userId)}`);
@@ -54,6 +54,42 @@ export async function presignAvatarUrl(userId: string): Promise<string | null> {
 	return data.url ? rewriteHost(data.url) : null;
 }
 
+/**
+ * Resolves the best available avatar URL for a user.
+ *
+ * Priority:
+ *   1. MinIO — if the user has uploaded a custom avatar it will be found here
+ *      (presigned, short-lived GET URL).
+ *   2. OAuth provider URL — stored in avatar_url when the account was created
+ *      via Google / GitHub OAuth (e.g. https://lh3.googleusercontent.com/...).
+ *      Returned as-is; the browser fetches it directly.
+ *
+ * Pass the raw `avatar_url` field from the PocketBase record as `storedValue`
+ * so this function can distinguish between a MinIO key and a remote URL without
+ * an extra DB round-trip.
+ *
+ * Returns null when neither source yields an avatar.
+ */
+export async function resolveAvatarUrl(
+	userId: string,
+	storedValue: string | null | undefined
+): Promise<string | null> {
+	// 1. Try MinIO first (custom upload takes priority over OAuth picture).
+	try {
+		const minioUrl = await presignAvatarUrl(userId);
+		if (minioUrl) return minioUrl;
+	} catch {
+		// MinIO unavailable — fall through to OAuth fallback.
+	}
+
+	// 2. Fall back to OAuth-provided picture URL if it looks like a remote URL.
+	if (storedValue && storedValue.startsWith('http')) {
+		return storedValue;
+	}
+
+	return null;
+}
+
 /**
  * Rewrites the MinIO host in a presigned URL to the public-facing URL.
  *

ui/src/lib/server/pocketbase.ts

@@ -541,6 +541,19 @@ export async function getUserByUsername(username: string): Promise<User | null>
 	return listOne<User>('app_users', `username="${username.replace(/"/g, '\\"')}"`);
 }
 
+/**
+ * Look up a user by their PocketBase record ID. Returns null if not found.
+ */
+export async function getUserById(id: string): Promise<User | null> {
+	const token = await getToken();
+	const res = await fetch(`${PB_URL}/api/collections/app_users/records/${encodeURIComponent(id)}`, {
+		headers: { Authorization: `Bearer ${token}` }
+	});
+	if (res.status === 404) return null;
+	if (!res.ok) return null;
+	return res.json() as Promise<User>;
+}
+
 /**
  * Look up a user by email. Returns null if not found.
  */