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.

docs/DESIGN.md

@@ -288,6 +288,10 @@ Wherever there is text, the user can select it and copy it, and no click action
   click-to-pause. Measured live: before this, a tap with the bar hidden both revealed it and paused. [Nielsen #3]
 - **The hide timer starts with playback,** not with the first touch (before, on touch, the bar stayed up until
   the first tap however long the video played).
+- **The bars stay up while the pointer rests on them** (F22, owner); leaving starts a fresh 3 s. YouTube and
+  Plex Web do the same: before, the row faded out from under a mouse parked on Next.
+- **Volume is the native `Slider`** (A6); the hand-drawn bar had no hover, focus, keyboard or screen-reader
+  state. A pointer drag gives the focus back, so Space and the arrows keep driving the player.
 - **The seek bar:** the track stays thin inside a 2.75rem (44px) hit area with `touch-action: none`, so a finger
   drag scrubs instead of panning; the scrub head is always visible on touch. Controls are 44 on touch. [WCAG 2.5.8]
 - **The Plex control set (C5, the owner's model):** one row that fits a portrait tablet.