fix(playback): force a transcode when the webview cannot decode the audio (DR-149, 0.4.8)

Advertising a webview-shaped profile (DR-148) was necessary but not
sufficient. Probing the server directly showed Jellyfin 10.11.5 enforces a
DirectPlayProfile's Container and VideoCodec — excluding either returns
SupportsDirectPlay:false with TranscodeReasons=ContainerNotSupported /
VideoCodecNotSupported — but ignores its AudioCodec entirely: an E-AC-3
track is still offered for direct play against a profile listing only
aac,flac,mp3,opus,vorbis. Neither a VideoAudio CodecProfile forbidding the
codec nor MaxAudioChannels:2 against a 6-channel track changes the answer,
so no profile the client can send fixes this and the picture plays silent.

The client therefore stops delegating a question it can answer itself. The
negotiated source's audio is checked against what the webview decodes, and
an undecodable track forces the existing h264/aac HLS transcode regardless
of the server calling direct play fine; direct_play and needs_transcoding
are corrected to match so the frontend and the reporting path agree with
the URL actually used. The track judged is the one that would be served —
the default, else the first — since a supported track further down is not
the one that plays. A source with no audio, or a codec the server did not
name, is left alone rather than transcoded on a guess.

Test-first: the new tests failed against the old behaviour before the
decision existed. Verified on a motorola edge 30 by the audio HAL, not by
ear — the same E-AC-3 episode logged isMusicActive=true once and 58
ACDB-LOADER lines under this build, against 0 and 0 on 0.4.6, where an AAC
file in the same session produced 16 and 116. No FATAL EXCEPTION, so R8 on
the signed release build is unaffected.

Also carries in-flight subtitle-track work authored in a parallel session
(subtitleTracks, VideoPlayer, player/media, bindings) at the user's
request, so the tag matches the APK verified on device.

CHANGELOG.md

@@ -6,6 +6,20 @@ Entries are grouped by the capability they change, not by commit. Requirement
 IDs in parentheses point at [docs/requirements.md](docs/requirements.md); the
 generated trace matrix lives in [docs/traceability.md](docs/traceability.md).
 
+## v0.4.8
+
+### 🐛 Fixes
+
+- **Video with an undecodable soundtrack now transcodes instead of playing
+  silent.** Advertising a webview-shaped profile (v0.4.7) turned out not to be
+  enough: Jellyfin 10.11.5 enforces a direct-play profile's container and video
+  codec but ignores its audio codec, offering an E-AC-3 track for direct play
+  against a profile listing only AAC — and no `CodecProfile` or channel limit
+  changes that. The client now checks the track it would actually be served
+  against what its renderer can decode and forces the h264/AAC HLS transcode
+  when it cannot, rather than trusting the negotiation.
+  (UR-004 → DR-149)
+
 ## v0.4.7
 
 ### 🐛 Fixes