feat(fullscreen): performance fixes + appearance settings

Adds no_compositing_mode Tauri command; frontend adds html.no-compositing on Linux to replace GPU-only CSS effects (backdrop-filter, filter, mask-image) with software-friendly equivalents.

Settings → Appearance → Fullscreen Player: toggle for artist portrait visibility + 0–80% dimming slider.

Fix: long words in lyric lines now wrap correctly.

src/App.tsx

@@ -88,6 +88,13 @@ function AppShell() {
     invoke<boolean>('is_tiling_wm_cmd').then(setIsTilingWm).catch(() => {});
   }, []);
 
+  useEffect(() => {
+    if (!IS_LINUX) return;
+    invoke<boolean>('no_compositing_mode').then(noComp => {
+      if (noComp) document.documentElement.classList.add('no-compositing');
+    }).catch(() => {});
+  }, []);
+
   useEffect(() => {
     const win = getCurrentWindow();
     // Check initial state (e.g. app launched maximised / already fullscreen).