fix: stop playback stutter and save failures via async yt-dlp, per-download OPFS workers, lazy playback blobs, GPU composite trims, and landscape pane scrolling

frontend/styles.css

@@ -1305,6 +1305,12 @@ input[type="range"]::-webkit-slider-thumb:hover { transform: scale(1.25); }
 @media (max-width: 1080px) {
   .body { flex-direction: column; }
   .list-pane { width: auto; border-left: none; border-top: 1px solid var(--line-soft); }
+  /* In the stacked layout both panes must be allowed to shrink below their
+     content height (flex min-height defaults to auto), or they overflow the
+     hidden .body instead of engaging their own scrollbars — on a landscape
+     phone that made "Up next" unreachable. */
+  .player-pane { min-height: 0; }
+  .list-pane { min-height: 0; }
 }
 
 /* ============================================================================
@@ -1878,6 +1884,31 @@ input[type="range"]::-webkit-slider-thumb:hover { transform: scale(1.25); }
   .hero-tagline { font-size: 13px; }
 }
 
+/* ============================================================================
+ * INSTALLED PWA ON TOUCH DEVICES — drop expensive full-screen composites
+ *
+ * The film-grain overlay (mix-blend-mode over the whole viewport), the fixed
+ * gradient wash, and the chrome backdrop-blurs all re-composite over the
+ * playing <video> every frame. On iPhones that GPU contention audibly
+ * stutters audio — backgrounding the PWA (which stops rendering) made
+ * playback smooth, which is how this was diagnosed. Same cuts as
+ * data-perf="on", applied automatically where they hurt most; desktop
+ * browsers and fine-pointer devices are untouched.
+ * ========================================================================== */
+@media (display-mode: standalone) and (pointer: coarse) {
+  body::before,
+  body::after { display: none; }
+  .topbar,
+  .bottom-nav,
+  .mini-bar-inner {
+    backdrop-filter: none;
+    -webkit-backdrop-filter: none;
+  }
+  .player-pane:not(.empty) .player-stage {
+    box-shadow: 0 0 0 1px var(--line) inset;
+  }
+}
+
 /* ============================================================================
  * PORTRAIT PWA — mobile app design refresh
  *