fix(playback): bound the device profile by the audio route's channels (DR-141)

MediaCodecList answers "can this device decode 5.1", which is not the
question that decides whether the user hears anything: a phone decodes an
AC-3 5.1 track happily and still has two channels to play it out of. The
DeviceProfile carried no MaxAudioChannels, so Jellyfin was free to
direct-play the multichannel track to a two-channel sink — silence or
dialogue folded into surround channels that go nowhere, depending on the
device.

Report media3 AudioCapabilities.maxChannelCount for the current route over
JNI alongside the codec lists, and bound the direct-play and transcoding
profiles (and the HLS URL's TranscodingMaxAudioChannels, previously
hardcoded to 2) by it. No codec is ever removed, so a device with genuine
surround output keeps direct-playing it. A missing or zero reading means
"route not yet established", not "no audio", and falls back to stereo.

docs/requirements.md

@@ -300,6 +300,7 @@ Internal architecture, components, and application logic.
 | DR-129 | A stream that stops delivering is recovered, not treated as terminal. Two failure shapes, because the streams differ. (a) *Phantom end* — the background audio-only handoff uses a progressive mp3 transcode over plain HTTP, chunked and therefore length-less, so a dropped connection reaches the player as end-of-input and ExoPlayer reports `STATE_ENDED` indistinguishably from the real end. The item's runtime is the only thing that can tell them apart: an end reported more than a tolerance short of it (comparing the *absolute* position — handoff base plus the player's relative position) is a truncation. Left unhandled, playback parked in `STATE_ENDED` and the next play intent from the lockscreen, notification or a Bluetooth reconnect seeks an ended player to position 0 — the user-visible "the episode randomly restarted". (b) *Recoverable error* — music (`/Audio/{id}/stream?Static=true`) and video (`/Videos/{id}/master.m3u8`) declare their length, so the player detects the truncation itself and raises an error; the frontend's handler stopped playback outright, turning a hiccup into silence. Both resume the current item **in place** (never via `play_item`, which would replace the queue with a single item and lose the album), the error path after a per-attempt backoff. Seekable streams are re-prepared at the URL they already have and seeked; the length-less transcode, which cannot be seeked, has `StartTimeTicks` rewritten into its existing URL so the user's audio-track selection survives and recovery needs no network round-trip. Only `Remote` sources qualify — a local file cannot fail from the network. A shared budget of consecutive attempts at the same position, refilled whenever playback progresses, stops an unreachable server from looping | Playback | UR-040, UR-004 | Done |
 | DR-130 | A backend's position and duration must survive the end of the file they describe. MPV exposes `time-pos`/`duration` as properties of the *loaded* file, so at EOF it unloads and both stop resolving — the accessors reported `0.0`/unknown at exactly the moment end-of-file handling asks where playback reached, and any position-versus-runtime check would have read every natural end as a truncation. The poll thread records the last reading and the accessors fall back to it. Linux resilience is layered on the same principle that the stream, not the player, is what failed: MPV is configured with ffmpeg reconnection (`stream-lavf-o`, `network-timeout`) so ordinary blips never surface, and `EndFile(ERROR)` — previously a bare log, which left playback halted while the UI still showed "playing" — is emitted as a *recoverable* error. Because MpvBackend is constructed before `PlayerController` exists, it cannot decide in-process like the Android JNI callback: the frontend echoes the error into `player_recover_stream`, which keeps the decision in Rust (the same shape as `PlaybackEnded` → `player_on_playback_ended`). Android reports errors it has already declined as *unrecoverable*, so the echo never asks twice | Playback | UR-004, UR-040 | Done |
 | DR-140 | An audio track is pinned only when the user picked one. Jellyfin's `MediaStream.Index` is global across every stream in a media source, so index 0 is the *video* stream on virtually all files — yet `AudioStreamIndex=0` was sent as "the first audio track" on the HLS transcode URL, the background audio-only handoff URL, the direct-play fallback URL, and the `PlaybackInfo` negotiation body. A server that honours the request literally then transcodes the video stream into the audio slot and the result plays as a picture with no sound; only servers that silently correct the index hid the bug, which is why it presented as "some videos have no audio". The parameter is now omitted whenever no track has been chosen, so the server resolves the source's `DefaultAudioStreamIndex`; an explicit selection from `player_switch_audio_track` is still carried through unchanged. On the `static=true` direct-play URL it is dropped outright — the original file is served untouched, so the parameter could only mislead | Playback | UR-004, UR-040 | Done |
+| DR-141 | One search input per screen, and the URL is the search's single source of truth. The header bar rendered only under `/library/**` and merely *navigated* to `/search` (DR-063), so a desktop search handed the user to a screen whose input was a different element — the header box cleared itself and vanished, and the page's own box took over mid-word. That page then re-derived its input from `?q=` against `library.searchQuery` on every store write, so the next keystroke re-ran the effect and snapped the text back to the query the header had sent (and a scope chip back to the URL's scope); entering from the bottom-nav Search tab skipped it only because the effect early-returned on an empty query. The bar now renders on `/search` too (`showHeaderSearch`) and is the sole md+ input — the page's own input is `md:hidden` — and on that route it republishes the query into the URL with `replaceState`, so a whole session of typing costs one history entry. The page *consumes* that URL once per distinct value (`seedFromSearchUrl` against a non-reactive `applied` marker) instead of continuously reconciling it, and the scope chips publish through the same URL so the bar and the chips cannot disagree. Landing on `/search` with a seeded query focuses the bar and puts the caret at the end, because the box the user was typing in belonged to the unmounted route | UI | UR-049, UR-054 | Done |
 | DR-093 | Traceability coverage gate derives its requirement denominators from `requirements.md` at run time rather than hardcoded literals: `countDefinedRequirements` counts an ID only where it leads a markdown table row (ignoring the "Traces To" column and prose) and deduplicates IDs listed both in the definition tables and in the §3 traceability matrix; `computeCoverage` reports the *intersection* of traced and defined IDs so an ID traced in code but absent from `requirements.md` is surfaced as `orphaned` instead of inflating the ratio past 100%. UT/IT test identifiers are excluded as a separate taxonomy. CI and `bun run traces:coverage` share this computation and fail on both a sub-threshold and an impossible >100% result | Tooling | - | Done |
 
 ---
@@ -508,6 +509,7 @@ Internal architecture, components, and application logic.
 | UT-117 | A background audio-only stream cut short resumes where it died instead of ending the episode; a real end still advances; the absolute position is compared against the runtime; retries at a stuck position give up. A recoverable error resumes music and video too, with growing backoff, leaving the rest of the queue intact and the seekable stream's URL untouched; local and DirectUrl sources are excluded | DR-129 | Done |
 | UT-121 | An EOF reads as the last observed timestamp, not zero: live readings win while the file is loaded, a not-yet-established duration is not recorded as a real zero, a seek updates the position before the next poll, and loading a new file clears the previous one's | DR-130 | Done |
 | UT-130 | Video and background-audio stream URLs omit `AudioStreamIndex` when no track was chosen, and carry the exact index when one was | DR-140 | Done |
+| UT-131 | The Episode Focus View hero offers a download control | DR-142 | Done |
 
 ### Integration Tests