fix(plex): player + card polish from UAT

- Player: control tooltips now open ABOVE the button (no downward viewport clip);
  keyboard use also reveals the auto-hidden controls (wake() on keydown); added a
  Download button that downloads the ORIGINAL physical file (no re-encode/repackage,
  Content-Disposition attachment via GET /stream/{rk}/file?download=1).
- Plex cards: hover affordance shows what a click does (Play / Resume / Open show)
  + a quick watched/unwatched toggle (stopPropagation, no playback) — mirrors the
  YT-feed card quick-actions. New plex i18n keys en/hu/de.
- Verified in a real browser: card hover Play overlay + watched toggle (marks watched
  without opening), player download button present, tooltip-above, keyboard reveals
  controls, correct durations (Enola Holmes 3 = 1:48:04).
- NOTE: 'The Three Diablos' showing 13:05 was NOT a bug — it is a 13-min short (file
  ffprobe = 785s); the 1h42m film is 'The Last Wish'.

frontend/src/lib/api.ts

@@ -1054,6 +1054,8 @@ export const api = {
       body: JSON.stringify({ status }),
     }),
   plexStreamFileUrl: (id: string): string => `/api/plex/stream/${encodeURIComponent(id)}/file`,
+  plexDownloadUrl: (id: string): string =>
+    `/api/plex/stream/${encodeURIComponent(id)}/file?download=1`,
   plexImageUrl: (id: string, variant?: "thumb" | "art"): string =>
     `/api/plex/image/${encodeURIComponent(id)}${variant === "art" ? "?variant=art" : ""}`,
   // --- admin: users & roles ---