ui: drop the Live view submenu; turn nav into a 64x64 icon rail

All grid/play/fullscreen submenu items are removed from every sidebar
(index, archive, settings, layout) — those controls now live in the live
grid footer. The sidebar becomes a narrow 72px rail and Live/Archive/Settings
render as 64x64 icon tiles (icon + small caption, active = inset red ring).
The layout.html gear (only link to /layout) is dropped with its submenu, so
the layout editor is now reachable by URL only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/index.html

@@ -10,17 +10,6 @@
   <div class="layout">
     <aside>
       <a class="nav-item active" href="/" data-nav="live"><span class="ico">▦</span>Live view</a>
-      <div class="subnav" id="live-subnav">
-        <a class="subitem subplay" id="play-toggle" href="#" title="Начать/остановить просмотр">⏹ Стоп</a>
-        <a class="subitem" data-grid="2" href="/?grid=2">4</a>
-        <a class="subitem" data-grid="3" href="/?grid=3">9</a>
-        <a class="subitem" data-grid="4" href="/?grid=4">16</a>
-        <a class="subitem" data-grid="5" href="/?grid=5">25</a>
-        <a class="subitem" data-grid="6" href="/?grid=6">36</a>
-        <a class="subitem" data-grid="7" href="/?grid=7">49</a>
-        <a class="subitem" data-grid="8" href="/?grid=8">64</a>
-        <a class="subitem subfs" id="fs-grid" href="#" title="Развернуть сетку на весь экран">⛶ Полный экран</a>
-      </div>
       <a class="nav-item" href="/archive" data-nav="archive"><span class="ico">🗄</span>Архив</a>
       <div class="aside-spacer"></div>
       <a class="nav-item" href="/settings" data-nav="settings"><span class="ico">⚙</span>Настройки</a>