feat(gui): surface SAM21 source + n_points in TrovaUtensile status bar

Status line on "Pianifica grasp" now shows source=sam21 / source=bbox_roi
(with fallback reason if any) plus n_points, so SAM21 vs fallback path is
visible at a glance without opening DevTools.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/app.js

@@ -311,7 +311,8 @@ $('planBtn').addEventListener('click', async () => {
     $('graspOut').textContent = JSON.stringify(r, null, 2);
     renderGraspLegend(lastDetections);
     drawGraspFrame(); drawCrop();
-    setStatus(`Plan ok · ${fmtTimings(r.timings_ms)}`, 'ok');
+    const src = r.source ? `source=${r.source}${r.sam21_fallback_reason ? ` (${r.sam21_fallback_reason})` : ''} · ` : '';
+    setStatus(`Plan ok · ${src}n=${r.n_points ?? '?'} · ${fmtTimings(r.timings_ms)}`, 'ok');
   } catch (e) { setStatus(e.message, 'err'); }
 });