feat(player): fullscreen "Listening Room" mode

Toggleable theater-scale player view that takes over the viewport
and amplifies the existing Studio Reference aesthetic — same fonts,
same copper/ink palette, just dialed up for immersive listening.

Layout & typography:
- Two-column centerfold: massive vinyl stage left (clamp(., 72vh, 720px)),
  editorial column right with Fraunces italic title at clamp(48px, 6.4vw,
  112px), Geist Mono console-style metadata strip, oversized timecodes,
  full-width amplitude spectrum.
- Mobile / portrait flips to vertical theater (vinyl top, masthead+
  transport below) at <=900px or any portrait orientation.

Ambient bloom:
- Duplicate of #album-art rendered behind everything at blur(110px)
  saturate(1.6) opacity(0.42) — paints the room in the record's color.
  Slow 28s drift animation. Light-theme variant at lower opacity.
- MutationObserver keeps bloom art in sync as tracks change.
- Vignette + edge darkening + subtle paper-grain veil frame the stage.

Interaction:
- Header button (corner-arrows-out icon) toggles; pressing 'F' anywhere
  outside text inputs also toggles; ESC exits.
- Native Fullscreen API requested as best-effort sugar on top of the
  CSS overlay (works on TV / tablet); CSS overlay alone covers the
  CSS-only fallback case (iOS Safari, embedded webviews).
- fullscreenchange listener mirrors OS-level exit back into the overlay.
- Auto-hide chrome + cursor after 2.5s idle, restored on mousemove.
- Focus moves to play/pause on enter; restored to invoking element on
  exit.
- Hides mini-player, tab bar, header, folio marks, and other tabs while
  active.

Motion:
- 320ms fade-in for the stage, 600ms vinyl rise, 1.4s bloom-in,
  staggered 80ms ladder for kicker -> title -> byline -> album -> meta
  -> spectrum -> transport. prefers-reduced-motion disables all.

i18n:
- player.fullscreen / player.fullscreen.exit / player.fullscreen.exit_short
  added to en.json and ru.json.

Files: index.html (header button + fs-chrome strip + fs-bloom layer),
styles.css (~360-line fullscreen block at end, scoped to body.is-
fullscreen-player), player.js (toggle + init + idle/key/observer
plumbing, ~170 lines), app.js (import + window export + init call).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

media_server/static/js/app.js

@@ -25,6 +25,7 @@ import {
     checkVisualizerAvailability, toggleVisualizer, applyVisualizerMode,
     loadAudioDevices, onAudioDeviceChanged,
     setupProgressDrag, updateUI, updatePlaybackState, stopPositionInterpolation,
+    togglePlayerFullscreen, initPlayerFullscreen,
 } from './player.js';
 
 // Layer 2: WebSocket
@@ -99,6 +100,8 @@ Object.assign(window, {
     toggleVisualizer,
     // Background
     toggleDynamicBackground,
+    // Fullscreen
+    togglePlayerFullscreen,
     // Auth
     authenticate, clearToken, manualReconnect,
     // Locale
@@ -156,6 +159,7 @@ window.addEventListener('DOMContentLoaded', async () => {
     // Initialize theme and accent color
     initTheme();
     initAccentColor();
+    initPlayerFullscreen();
 
     // Register service worker for PWA installability
     if ('serviceWorker' in navigator) {