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/index.html

@@ -75,11 +75,15 @@
         </div>
     </div>
 
+    <!-- Folio marks at page corners -->
+    <span class="folio tl"><span class="status-dot" id="status-dot" aria-live="polite"></span><span data-i18n="header.connected">Connected</span> · <span id="folio-host">Local 8765</span></span>
+    <span class="folio tr"><span data-i18n="header.volume">Vol. I</span> — <span data-i18n="header.edition">Studio Reference</span> · <span id="version-label"></span></span>
+
     <div class="container">
         <header>
-            <div style="display: flex; align-items: center; gap: 0.5rem;">
-                <span class="status-dot" id="status-dot" aria-live="polite"></span>
-                <span class="version-label" id="version-label"></span>
+            <div class="brand">
+                <span class="brand-name" data-i18n="app.title">Media Server</span>
+                <span class="brand-sub" data-i18n="header.edition_sub">Studio Reference Edition</span>
             </div>
             <div class="header-toolbar">
                 <div id="headerLinks" class="header-links"></div>
@@ -153,9 +157,6 @@
         </div>
 
         <div class="player-container" data-tab-content="player" role="tabpanel" id="panel-player">
-            <span class="folio tl"><span data-i18n="player.folio_left">Now Spinning</span> · <span id="folio-version">v—</span></span>
-            <span class="folio tr" data-i18n="player.folio_right">Vol. I — Studio Reference</span>
-
             <div class="player-layout now-playing">
 
                 <!-- Vinyl stage with album art as label -->
@@ -280,15 +281,12 @@
                         </div>
                     </div>
 
-                    <!-- Player toggles -->
+                    <!-- Audio visualizer toggle (button shown by JS only when supported) -->
                     <div class="source-info">
                         <span class="source-label">
                             <span class="vinyl-mode-label" data-i18n="player.modes">Modes</span>
                         </span>
                         <div class="player-toggles">
-                            <button class="vinyl-toggle-btn" onclick="toggleVinylMode()" id="vinylToggle" data-i18n-title="player.vinyl" title="Vinyl mode">
-                                <svg viewBox="0 0 24 24" width="16" height="16"><circle cx="12" cy="12" r="10" fill="none" stroke="currentColor" stroke-width="1.5"/><circle cx="12" cy="12" r="3" fill="currentColor"/><circle cx="12" cy="12" r="6.5" fill="none" stroke="currentColor" stroke-width="0.5" opacity="0.5"/></svg>
-                            </button>
                             <button class="vinyl-toggle-btn" onclick="toggleVisualizer()" id="visualizerToggle" data-i18n-title="player.visualizer" title="Audio visualizer" style="display:none">
                                 <svg viewBox="0 0 24 24" width="16" height="16"><path fill="currentColor" d="M3 18h2v-8H3v8zm4 0h2V6H7v12zm4 0h2V2h-2v16zm4 0h2v-6h-2v6zm4 0h2V9h-2v9z"/></svg>
                             </button>