fix(plex): the player's stage follows the tablet toolbar, and its bands stay out of a double-tap

- The stage is sized in dvh (80dvh × 1.25 windowed, 100dvh fullscreen); the viewport-units
  contract no longer exempts the player.
- A tap that reveals the bands keeps them pointer-events-none for the double-tap window, so the
  second tap of a skip at the bottom is not a seek.
- An arrow on the volume slider wakes the bands, and a keyboard focus in a band holds them
  (`holdOnFocus`, `:focus-visible` only, so a clicked button does not pin the bar).
- Next stays mounted (disabled) while the next episode's detail loads, keeping the focus.

frontend/src/lib/viewportUnits.contract.test.ts

@@ -18,14 +18,9 @@ function sources(): Array<[string, string]> {
   return walk(new URL("../", import.meta.url), "");
 }
 
-// The Plex player's stage is sized with the 80vh × 1.25 zoom trick. It changes in S3f, where the
-// players are re-fitted for touch and verified by playing them on the tablet.
-const PENDING_S3F = new Set(["components/PlexPlayer.tsx"]);
-
 describe("viewport units", () => {
   it("are dynamic: no h-screen / min-h-screen, no static vh", () => {
     const hits = sources()
-      .filter(([name]) => !PENDING_S3F.has(name))
       .filter(([, src]) => /\b(?:min-|max-)?h-screen\b|\d(?:\.\d+)?vh\b/.test(src))
       .map(([name]) => name);
     expect(hits).toEqual([]);