fix(ui): close gaps with Studio Reference mockup

Side-by-side comparison surfaced several layout regressions vs. the
mockup. This commit lands all of them at once.

Header
- Restore centered "Media Server / Studio Reference Edition" wordmark
  in italic Fraunces
- Move folio marks to fixed page corners (visible on every tab):
  TL = green pulse + "Connected · Local 8765"
  TR = "Vol. I — Studio Reference · v0.x.x"
- Replace boxed version-label badge with copper mono inline in folio.tr
- Reduce header-to-content gap (container padding-top 28→56 with the
  folio now anchored above)

Player view
- Spectrum bars: smaller height (32px), centered with max-width so
  they don't span the whole right column
- Spectrogram canvas: hidden by default (opacity 0); reveals only when
  visualizer toggle is active. No more leaking into bottom-left.
- VU cluster volume controls: strip legacy box (background, padding,
  border-radius); compact stacked layout with thin slider, small mute
  button, mono "VOL · XX%" readout
- Disable legacy applyVinylMode() — the .vinyl class added a SECOND
  rotation animation on top of the structural .vinyl-stage spin,
  causing visible compounding. Vinyl is now purely structural.

Toggles
- Remove vinyl mode toggle button (vinyl is always on)
- Keep audio visualizer (spectrum vis) toggle — still shown by JS
  when supported

Mini player
- Force always-visible on non-player tabs regardless of scroll, by
  short-circuiting setMiniPlayerVisible when activeTab !== 'player'

i18n
- New keys: header.connected, header.volume, header.edition,
  header.edition_sub
- Removed unused: player.folio_left, player.folio_right
- en.json + ru.json updated

media_server/static/locales/en.json

@@ -21,8 +21,10 @@
   "player.no_media": "No media playing",
   "player.kicker": "Now Playing",
   "player.modes": "Modes",
-  "player.folio_left": "Now Spinning",
-  "player.folio_right": "Vol. I — Studio Reference",
+  "header.connected": "Connected",
+  "header.volume": "Vol. I",
+  "header.edition": "Studio Reference",
+  "header.edition_sub": "Studio Reference Edition",
   "meta.state": "State",
   "meta.source": "Source",
   "meta.elapsed": "Elapsed",

media_server/static/locales/ru.json

@@ -21,8 +21,10 @@
   "player.no_media": "Медиа не воспроизводится",
   "player.kicker": "Сейчас играет",
   "player.modes": "Режимы",
-  "player.folio_left": "Сейчас играет",
-  "player.folio_right": "Том I — Studio Reference",
+  "header.connected": "Подключено",
+  "header.volume": "Том I",
+  "header.edition": "Studio Reference",
+  "header.edition_sub": "Studio Reference Edition",
   "meta.state": "Состояние",
   "meta.source": "Источник",
   "meta.elapsed": "Прошло",