unify single user and multi user behaviour

site/src/components/StatsView.svelte

@@ -4,6 +4,9 @@
   import { formatDistance, formatDuration, sportIcon, sportColor, sportLabel } from '../lib/format';
   import { loadIndex } from '../lib/dataloader';
 
+  /** Explicit index URL — use for per-user stats pages in multi-user mode. */
+  export let indexUrl: string = '';
+
   const PAGE_YEARS = 4;
 
   let all: ActivitySummary[] = [];
@@ -31,7 +34,7 @@
     page  = parseInt(params.get('page') ?? '0', 10) || 0;
     mounted = true;
     try {
-      const index = await loadIndex(import.meta.env.BASE_URL);
+      const index = await loadIndex(import.meta.env.BASE_URL, indexUrl || undefined);
       all = index.activities.filter(a => a.privacy !== 'private' && a.distance_m);
     } catch (e: any) {
       error = e.message;