feat: Apple glass gray theme, lower live latency, audio fix, remote focus memory

Theme — replace the near-black "Warm Cinema" palette with a neutral
"Apple Glass Gray" system: graphite surfaces (#26262C base, lighter
containers), Apple-white text, Apple system blue accent, white glass
borders/highlights. Noticeably less dark overall; light theme moves
from kraft paper to iOS light gray. All AppColors names kept so no
call site changes.

Player latency — live buffering drops from 8s cache / 10s readahead /
150MB to 3s / 5s / 60MB, keeping enough headroom for network jitter
while staying much closer to the live edge.

Audio — the forced audio filter chain
(af=lavrresample,format=channels=stereo:sample_fmts=s16) mixed FFmpeg
and mpv syntax; when it failed to init for a channel's codec, mpv
muted the stream entirely. Replaced by mpv's native
audio-channels=stereo downmix and AO-negotiated output format. Probe
caps raised (2MB/3s) so late-declared audio tracks (AAC-LATM) are
detected without slowing healthy streams.

Remote control — the player OSD now remembers the last focused button
and restores focus to it whenever the OSD reopens (arrows, OK) and
across channel switches, so one press re-zaps instead of five. On
live TV, OK with hidden controls only reopens the OSD instead of
pausing the stream.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0156exq7fejVrD3HKU3MmS8X

lib/mobile/widgets/tv_focusable.dart

@@ -163,7 +163,7 @@ class _TVFocusableState extends State<TVFocusable> {
                             offset: const Offset(0, 6),
                           ),
                           const BoxShadow(
-                            color: Color(0x59D9541F), // Ember glow
+                            color: Color(0x590A84FF), // Apple blue glow
                             blurRadius: 12,
                             spreadRadius: 0,
                           ),