perf(fs-player): cut CPU under WebKitGTK software compositing

WebKitGTK on Linux runs with WEBKIT_DISABLE_COMPOSITING_MODE=1, so every
GPU-only effect is software-rasterised per frame. The fullscreen player
piled up large blur shadows, per-line scale transforms, oversized
radial-gradients with color-mix() and a 60 fps rAF spring on top — CPU
saturated and FPS dropped to ~10.

Linux-only via existing html.no-compositing class:
- Apple-style lyrics: drop transform: scale and 48 px / 32 px text-shadow
- Rail-style lyrics: drop 28 px text-shadow + scaleX
- Track title: 40 px glow → 6 px drop-shadow
- Album art wrap + play button: drop accent-coloured outer glows
- Mesh blobs: flatten 130 % radial-gradient + color-mix to solid #06060e
  and remove the 400 ms background transition
- Portrait wrap: drop translateZ(0) GPU-layer hint
- FS art: instant cover swap (no opacity crossfade)
- SpringScroller: replace rAF spring with native scrollTo({behavior:'smooth'})
- FsSeekbar: cache last applied values, skip identical DOM writes

Dynamic accent on title / seekbar / play button is preserved.

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

src/styles/components.css

@@ -3856,6 +3856,22 @@
 html.no-compositing .fsr-lyrics-overlay { -webkit-mask-image: none; mask-image: none; }
 html.no-compositing .fsr-lyrics-rail    { will-change: auto; }
 
+/* Apple-style FS lyrics — strip GPU-only effects.
+   Without compositing, transform: scale() on every line forces a per-line
+   software repaint on each active-line change, and the 48 px / 32 px blur
+   text-shadows repaint on every word tick. Replace with opacity + colour,
+   which are cheap text-only repaints. */
+html.no-compositing .fsa-lyric-line {
+  transform: none;
+  transition: color 380ms cubic-bezier(0.25, 0.46, 0.45, 0.94),
+              opacity 380ms cubic-bezier(0.25, 0.46, 0.45, 0.94);
+}
+html.no-compositing .fsa-lyric-line.fsal-past   { transform: none; }
+html.no-compositing .fsa-lyric-line.fsal-active { transform: none; text-shadow: none; }
+html.no-compositing .fsa-lyric-line.fsal-active .fsa-lyric-word.active {
+  text-shadow: none;
+}
+
 /* ── no-compositing overrides ─────────────────────────────────────────────────
    Applied only when WEBKIT_DISABLE_COMPOSITING_MODE=1 is set (Arch Linux etc).
    Replaces GPU-only effects (backdrop-filter, CSS filter, mask-image) with
@@ -3880,10 +3896,19 @@ html.no-compositing .fs-portrait {
 }
 
 /* Portrait wrap: replace mask-image fade with a pseudo-element overlay gradient.
-   pointer-events: none on wrap means the overlay never blocks clicks. */
+   pointer-events: none on wrap means the overlay never blocks clicks.
+   Also drop translateZ(0) — useless GPU layer hint without a compositor. */
 html.no-compositing .fs-portrait-wrap {
   -webkit-mask-image: none;
   mask-image: none;
+  transform: none;
+}
+
+/* FS art crossfade: opacity transition compositing is GPU-cheap, software-expensive.
+   Snap instantly between covers; visually a hard cut, but the previous layer is
+   replaced before the user can really notice. */
+html.no-compositing .fs-art {
+  transition: none;
 }
 html.no-compositing .fs-portrait-wrap::before {
   content: '';
@@ -3901,12 +3926,16 @@ html.no-compositing .fs-portrait-wrap::before {
 
 /* Lyrics fade overlays: gradient-only, no backdrop-filter — fine in no-compositing */
 
-/* Mesh blobs: stop animations — in software mode each frame composites surfaces
-   larger than the screen (blob-a is 130 × 130 % of the viewport); on high-DPI
-   displays this saturates the CPU and drops the player to ~10 FPS.
-   Static gradients are preserved; only the slow pan animation is removed. */
+/* Mesh blobs: stop animations + flatten to a solid dark fill.
+   Even static, the 130 × 130 % radial-gradient with color-mix() is recomputed
+   on every paint, and the `transition: background 400ms` on accent change
+   re-rasterises the giant surface for nearly half a second per track switch.
+   Atmosphere is sacrificed; the dynamic accent is preserved on title /
+   seekbar / controls via their own var(--dynamic-fs-accent) bindings. */
 html.no-compositing .fs-mesh-blob {
   animation: none;
+  background: #06060e;
+  transition: none;
 }
 
 /* Seekbar played bar: remove box-shadow — its width changes on every playback
@@ -3915,6 +3944,45 @@ html.no-compositing .fs-seekbar-played {
   box-shadow: none;
 }
 
+/* Track title: drop the 40 px text-shadow glow — paints a giant blur on a
+   clamp(28–68 px) font and re-rasterises whenever anything around it
+   redraws (cluster updates, seekbar tick, dynamic accent change). */
+html.no-compositing .fs-track-title {
+  text-shadow: 0 2px 6px rgba(0, 0, 0, 0.65);
+  transition: color 200ms ease-in-out;
+}
+
+/* Album art wrap: replace the accent-coloured outer glow with a flat
+   shadow. The 28 px blur was repainting every accent change. */
+html.no-compositing .fs-art-wrap {
+  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.7), 0 0 0 1px rgba(255, 255, 255, 0.07);
+  transition: none;
+}
+
+/* Play button: drop accent glow + hover filter. Keep flat dark shadow only. */
+html.no-compositing .fs-btn-play {
+  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.55);
+}
+html.no-compositing .fs-btn-play:hover {
+  filter: none;
+  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.65);
+}
+
+/* Rail-style FS lyrics: same problems as Apple style — 28 px text-shadow
+   blur on every active line + every active word, plus per-line transform
+   scaleX. Strip them; rail still scrolls fine via the parent translateY. */
+html.no-compositing .fsr-lyric-line {
+  transition: color 280ms ease;
+  transform: none;
+}
+html.no-compositing .fsr-lyric-line.fsrl-active {
+  text-shadow: none;
+  transform: none;
+}
+html.no-compositing .fsr-lyric-line.fsrl-active .fsr-lyric-word.active {
+  text-shadow: none;
+}
+
 /* Chat */
 .chat-popup {
   position: absolute;