feat(design): Warm Cinema redesign + fast-start players

Full visual overhaul from Cyber-Cinematic Glass to "Warm Cinema":
warm charcoal (#0B0908), cream (#F3E9DF), ember (#D9541F).
Fraunces (editorial serif) for display, Karla for body/UI.

Design
- app_colors: new palette, all existing token names preserved,
  plus posterScrim/heroScrim gradients and lift()/emberFocus() shadows
- app_theme: new type scale, tighter radii, 20+ component themes
- mobile_theme aligned on the same tokens
- glass_container: opaque layered surfaces replace glassmorphism;
  adds GlassCard (hover + remote-focus states) and CinemaBackdrop
- players and boot splash restyled (film-leader motif, no web fonts)

Performance
- remove every BackdropFilter (33 call sites): backdrop blur forced a
  full framebuffer read per frame per card, the main scroll jank source
- bundle Fraunces/Karla as assets: google_fonts no longer fetches from
  fonts.gstatic.com at startup
- drop the blocking hls.js CDN script from index.html; no Dart code
  ever used it, only the player iframes need it
- self-host hls.js/mpegts.js and load them on demand, so ~213 KB of
  mpegts is never downloaded for HLS streams
- bound image decode size on 10 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)
- event-driven start instead of a 200 ms buffer poll plus a 1.5 s wait
- initialLiveManifestSize 3 -> 1, liveSyncDurationCount 10 -> 2,
  startFragPrefetch on, testBandwidth off
- MPEG-TS initial stash 512 KB -> 64 KB
- adaptive escalation fast -> balanced -> safe on repeated stalls
  (60 s rolling window), applied live for HLS so there is no visible cut

Pre-existing build breakage fixed along the way
- undefined AppColors.shimmer, AppTheme.durationXs and spacing8/12/16/32
- broken relative imports in channel_card and quality_selector_widget
- missing GlassCard widget and hasBorder/showShadow parameters

Also resolves a leftover unmerged .claude/settings.local.json by
keeping the remote version.

Still broken (pre-existing, dead code, not reachable from main.dart):
recommendations_provider.dart and continue_watching_widget.dart import
a models/playlist.dart that no longer exists.

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.inter(
+                    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.inter(
+                    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.inter(
+                                      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.inter(
+                    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.inter(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.inter(color: AppColors.textSecondary),
+        labelStyle: GoogleFonts.karla(color: AppColors.textSecondary),
         prefixIcon: Icon(icon, color: AppColors.textSecondary),
         suffixIcon: suffix,
         filled: true,