fix(player): the Plex bars hold while hovered, volume is the native slider, tooltips no longer re-layer the row (E28)

- F22: the control bar faded out from under a mouse parked on it; the hide timer
  now waits while the pointer is on either band and re-arms on leave (test seen
  RED by disabling the hold).
- The hand-drawn volume bar broke DESIGN.md A6 (native sliders): it had no hover,
  focus, keyboard or screen-reader state. It is the Slider primitive now; a
  pointer drag blurs it so Space and the arrows keep driving the player.
- The control tooltips are composited from mount (will-change: opacity): a fade
  that promoted one on hover re-layered its neighbours under the player's
  scale(1.25), and the whole row shimmered.

frontend/src/lib/plexPlayerHooks.ts

@@ -70,24 +70,36 @@ export function useFullscreen(wrapRef: RefObject<HTMLElement | null>): {
 // 3s hide timer. Reads the caller's live refs so the timer callback sees fresh state without a
 // closure rebuild: barAutoHide (per-user "never auto-hide" setting), whether a menu is open (keep the
 // bar up so it can't vanish mid-choice), and the <video> paused state (a paused video keeps the bar).
+// `holdOnHover` is the pointer resting on the chrome: the bar stays while it is there (as on YouTube
+// and Plex Web — E28 F22, it used to fade out from under a mouse parked on Next), and leaving it
+// starts a fresh 3 s.
 export function useControlsVisibility(opts: {
   barAutoHideRef: RefObject<boolean>;
   menuOpenRef: RefObject<boolean>;
   videoRef: RefObject<HTMLVideoElement | null>;
-}): { uiVisible: boolean; wake: () => void } {
+}): { uiVisible: boolean; wake: () => void; holdOnHover: (over: boolean) => void } {
   const { barAutoHideRef, menuOpenRef, videoRef } = opts;
   const [uiVisible, setUiVisible] = useState(true);
   const hideTimer = useRef<number | null>(null);
+  const hovered = useRef(false);
   const wake = useCallback(() => {
     setUiVisible(true);
     if (hideTimer.current) window.clearTimeout(hideTimer.current);
     if (!barAutoHideRef.current) return; // per-user setting: never auto-hide the control bar
     hideTimer.current = window.setTimeout(() => {
       // Keep the controls up while the audio/subtitle menu is open, else it would vanish mid-choice.
-      if (!videoRef.current?.paused && !menuOpenRef.current) setUiVisible(false);
+      if (!videoRef.current?.paused && !menuOpenRef.current && !hovered.current)
+        setUiVisible(false);
     }, 3000);
   }, [barAutoHideRef, menuOpenRef, videoRef]);
-  return { uiVisible, wake };
+  const holdOnHover = useCallback(
+    (over: boolean) => {
+      hovered.current = over;
+      if (!over) wake();
+    },
+    [wake],
+  );
+  return { uiVisible, wake, holdOnHover };
 }
 
 // Periodic + on-unmount progress checkpoint. Reads live position/duration through refs (owned by the