feat(design): Warm Cinema theme + event-driven adaptive players

Replaces the Projector Noir palette with "Warm Cinema" and rebuilds the
web players around a shared, event-driven engine.

Design
- app_colors: warm charcoal (#0B0908), cream (#F3E9DF), ember (#D9541F);
  adds posterScrim/heroScrim gradients, lift()/emberFocus() shadows,
  const cream-alpha tokens replacing Colors.whiteNN, and primaryFill,
  a deeper ember reserved for text-bearing fills so white labels clear
  the 4.5:1 AA threshold that #D9541F alone does not
- app_theme / mobile_theme: Fraunces (display serif) + Karla (body),
  tighter radii, 20+ component themes
- glass_container: opaque layered surfaces replace the blurred glass
- themed_loading_screen restyled; players and boot splash follow

Performance
- drop every BackdropFilter: backdrop blur forced a full framebuffer
  read per frame per card, the main source of scroll jank
- bundle Fraunces/Karla as assets so google_fonts stops fetching from
  fonts.gstatic.com at startup
- bound image decode size on 12 sites: a 40-poster grid drops from
  ~240 MB to a few tens of MB of GPU memory

Players (new shared engine: web/xf-player-core.js)
- start on media events instead of polling the buffer every 100-200 ms
- hls.js/mpegts.js loaded on demand, so ~213 KB of mpegts is never
  fetched for HLS streams
- liveSyncDurationCount 10 -> 2, startFragPrefetch on, testBandwidth
  off, MPEG-TS initial stash 512 KB -> 64 KB
- adaptive escalation fast -> balanced -> safe after repeated stalls in
  a 60 s window, applied live for HLS so there is no visible cut

Preserved from the recent streaming work on main: server-side quality
selection, stable player viewId, the turbo direct MPEG-TS path, vendored
library cache headers and the CI/Docker changes. Only the theme layer and
the player front-end were replaced; GlassCard stays in ui_components.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/features/admin/screens/admin_panel.dart

@@ -152,7 +152,7 @@ class _AdminContentState extends ConsumerState<AdminContent>
                 const SizedBox(width: 8),
                 Text(
                   label,
-                  style: GoogleFonts.instrumentSans(
+                  style: GoogleFonts.karla(
                     fontWeight: FontWeight.w600,
                     fontSize: 14,
                     color: isSelected ? AppColors.textPrimary : AppColors.textSecondary,
@@ -265,7 +265,7 @@ class _PlaylistsTab extends ConsumerWidget {
                                 style: Theme.of(context)
                                     .textTheme
                                     .titleMedium
-                                    ?.copyWith(color: Colors.white),
+                                    ?.copyWith(color: AppColors.onSurface),
                               ),
                               const SizedBox(height: 4),
                               Text(
@@ -273,7 +273,7 @@ class _PlaylistsTab extends ConsumerWidget {
                                 style: Theme.of(context)
                                     .textTheme
                                     .bodyMedium
-                                    ?.copyWith(color: Colors.white60),
+                                    ?.copyWith(color: AppColors.onSurface54),
                               ),
                             ],
                           ),
@@ -282,7 +282,7 @@ class _PlaylistsTab extends ConsumerWidget {
                           children: [
                             IconButton(
                               icon: const Icon(Icons.edit_outlined, size: 20),
-                              color: Colors.white70,
+                              color: AppColors.onSurfaceVariant,
                               onPressed: () =>
                                   _showPlaylistDialog(context, ref, playlist),
                               tooltip: 'Edit',
@@ -544,7 +544,7 @@ class _UsersTab extends ConsumerWidget {
                                     style: Theme.of(context)
                                         .textTheme
                                         .titleMedium
-                                        ?.copyWith(color: Colors.white),
+                                        ?.copyWith(color: AppColors.onSurface),
                                   ),
                                   if (user.isAdmin) ...[
                                     const SizedBox(width: 8),
@@ -576,7 +576,7 @@ class _UsersTab extends ConsumerWidget {
                                 style: Theme.of(context)
                                     .textTheme
                                     .bodyMedium
-                                    ?.copyWith(color: Colors.white60),
+                                    ?.copyWith(color: AppColors.onSurface54),
                               ),
                             ],
                           ),
@@ -584,7 +584,7 @@ class _UsersTab extends ConsumerWidget {
                         PopupMenuButton<String>(
                           icon: const Icon(
                             Icons.more_vert,
-                            color: Colors.white70,
+                            color: AppColors.onSurfaceVariant,
                           ),
                           color: AppColors.surface,
                           shape: RoundedRectangleBorder(