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/auth/screens/login_screen.dart

@@ -144,7 +144,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                   // Title
                   Text(
                     'XtremFlow',
-                    style: GoogleFonts.instrumentSans(
+                    style: GoogleFonts.karla(
                       fontSize: 42,
                       fontWeight: FontWeight.w700,
                       color: AppColors.textPrimary,
@@ -154,7 +154,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                   const SizedBox(height: 8),
                   Text(
                     'Sign in to sync your playlists',
-                    style: GoogleFonts.instrumentSans(
+                    style: GoogleFonts.karla(
                       fontSize: 18,
                       color: AppColors.textSecondary,
                       fontWeight: FontWeight.w400,
@@ -266,7 +266,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                                     )
                                   : Text(
                                       'Sign In',
-                                      style: GoogleFonts.instrumentSans(
+                                      style: GoogleFonts.karla(
                                         color: AppColors.primary,
                                         fontSize: 18,
                                         fontWeight: FontWeight.w600,
@@ -282,7 +282,7 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
                   const SizedBox(height: 32),
                   Text(
                     'Default: admin / admin',
-                    style: GoogleFonts.instrumentSans(
+                    style: GoogleFonts.karla(
                       fontSize: 14,
                       color: AppColors.textTertiary,
                     ),
@@ -310,13 +310,13 @@ class _LoginScreenState extends ConsumerState<LoginScreen> {
     return TextFormField(
       controller: controller,
       obscureText: obscureText,
-      style: GoogleFonts.instrumentSans(fontSize: 18, color: AppColors.textPrimary),
+      style: GoogleFonts.karla(fontSize: 18, color: AppColors.textPrimary),
       autofocus: autofocus,
       textInputAction: nextFocus ? TextInputAction.next : TextInputAction.done,
       onFieldSubmitted: isLast ? (_) => onSubmitted?.call() : null,
       decoration: InputDecoration(
         labelText: label,
-        labelStyle: GoogleFonts.instrumentSans(color: AppColors.textSecondary),
+        labelStyle: GoogleFonts.karla(color: AppColors.textSecondary),
         prefixIcon: Icon(icon, color: AppColors.textSecondary),
         suffixIcon: suffix,
         filled: true,