Echo thumbnails fade in via timeout, not rAF

The 'shown' class only needs a later tick for the opacity transition
to run - requestAnimationFrame never fires in headless engines
(caught in hwatu verification), and a timeout is equivalent in real
browsers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

gesture.js

@@ -254,7 +254,10 @@ class GestureWidget {
         const ctx = thumb.getContext('2d');
         ctx.scale(dpr, dpr);
         this.drawPath(ctx, msg.path, rect.width, rect.height, this.theme().echo, 1.5, 0.15);
-        requestAnimationFrame(() => thumb.classList.add('shown'));
+        // A timeout, not requestAnimationFrame: the class must land on
+        // a later tick for the opacity transition to run, and rAF
+        // doesn't tick at all in headless engines.
+        setTimeout(() => thumb.classList.add('shown'), 30);
     }
 
     // ── Rendering ──────────────────────────────────────────────────