live: double-click solos a cell to full screen (fullscreen mode)

Double-clicking a grid cell now maximizes that camera ("solo") via a CSS
class on the grid instead of putting the tile into the browser Fullscreen
API. In fullscreen the soloed camera fills the screen; double-clicking
again returns to the grid (staying fullscreen). From windowed mode the
gesture also enters fullscreen so the camera fills the screen. ESC exits
fullscreen natively; on exit the solo state is cleared.

VERSION -> 0.0.121.

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

frontend/static/style.css

@@ -158,6 +158,9 @@ input[type="date"], input[type="number"], select {
   background: #000; overflow: hidden;
   grid-auto-rows: 1fr; grid-auto-columns: 1fr;   /* все дорожки строго равны */
 }
+/* «Соло»: одна камера на весь экран (двойной клик по ячейке в полноэкранном режиме) */
+.grid.solo { grid-template-columns: 1fr !important; grid-template-rows: 1fr !important; }
+.grid.solo > .tile:not(.solo) { display: none; }
 .tile {
   position: relative; background: #05070a; border: 1px solid var(--border);
   display: flex; align-items: center; justify-content: center; overflow: hidden;