Phone PWA: no backdrop blurs over video, cap auto quality at 480p on touch phones

frontend/app.js

@@ -3032,9 +3032,13 @@ function chooseQuality() {
     const match = qs.find((q) => q.label === pref);
     if (match) return match;
   }
-  // auto: best quality at or below 720p, else the lowest available.
+  // auto: best quality at or below 720p (480p on touch phones, where a lossy
+  // link rebuffers the picture while the separate audio keeps playing),
+  // else the lowest available.
+  let cap = 720;
+  try { if (matchMedia('(pointer: coarse)').matches && Math.min(screen.width, screen.height) < 600) cap = 480; } catch {}
   const sorted = [...qs].sort((a, b) => b.height - a.height);
-  return sorted.find((q) => q.height <= 720) || sorted[sorted.length - 1];
+  return sorted.find((q) => q.height <= cap) || sorted[sorted.length - 1];
 }
 
 function buildQualityMenu() {