unify single user and multi user behaviour

site/src/lib/dataloader.ts

@@ -161,10 +161,16 @@ export async function loadActivity(
 /**
  * Load athlete profile. Athlete data is not stored locally yet, so this is
  * always a network fetch with a graceful null on failure.
+ *
+ * @param baseUrl    Site base URL (used to build the default path)
+ * @param athleteUrl Explicit full URL — use for per-user pages in multi-user mode
  */
-export async function loadAthlete(baseUrl: string): Promise<Record<string, unknown> | null> {
+export async function loadAthlete(
+  baseUrl: string,
+  athleteUrl?: string,
+): Promise<Record<string, unknown> | null> {
   try {
-    return await fetchJSON(`${baseUrl}data/athlete.json`);
+    return await fetchJSON(athleteUrl ?? `${baseUrl}data/athlete.json`);
   } catch {
     return null;
   }