fix(nests): G4+G5 plumb catalog sampleRate through decoder + AudioTrack

G4: Audit-9 (catalog-driven decoder reconfig) plumbed numberOfChannels
end-to-end but left sampleRate hardcoded at AudioFormat.SAMPLE_RATE_HZ
in MediaCodecOpusDecoder.buildOpusIdHeader / buildFormat and in
AudioTrackPlayer's MinBufferSize / 250 ms target / setSampleRate
calls. For Opus this is benign in practice — Codec2 always emits
48 kHz PCM regardless of OpusHead inputSampleRate — but hardcoding
the constant means a future codec or container variant whose
decoder DOES respect input sample rate would mis-clock playback.
And the OpusHead identification header should match what the
catalog declares either way.

Thread sampleRate alongside channelCount through every layer:

  - MediaCodecOpusDecoder constructor takes
    `sampleRate: Int = AudioFormat.SAMPLE_RATE_HZ`. buildFormat
    and buildOpusIdHeader both take it as a parameter.

  - AudioTrackPlayer constructor takes the same. Used in
    AudioTrack.getMinBufferSize, the 250 ms-equivalent target
    bytes calculation (`(sampleRate / 4) * BYTES_PER_SAMPLE *
    channelCount`), AndroidAudioFormat.Builder.setSampleRate, and
    the diagnostic log.

  - decoderFactory and playerFactory in NestViewModel become
    `(channelCount: Int, sampleRate: Int) -> ...`.

  - awaitDecoderChannelCount → awaitAudioPipelineConfig, returning
    a private `AudioPipelineConfig(channelCount, sampleRate)`
    struct so openSubscription handles both fields uniformly.
    `sampleRate` falls back to AudioFormat.SAMPLE_RATE_HZ on
    timeout / non-positive declaration with a warning log.

  - NestViewModelFactory + NestViewModelTest updated to the
    two-arg factory shape.

G5: documented the SUBSCRIBE_BUFFER safety budget on
CATALOG_AWAIT_TIMEOUT_MS's kdoc. With the current 500 ms timeout +
SUBSCRIBE_BUFFER = 64-frame DROP_OLDEST flow + 50 fps Opus, at
most 25 frames buffer during the wait — leaving ≥ 39 frames of
margin (≈ 780 ms) before the oldest frame would be evicted. Even
at the production framesPerGroup = 50 (1 group/sec) cadence this
never trips during normal startup. No code change; just pinning
the rationale so a future timeout bump is checked against the
buffer size.

https://claude.ai/code/session_014JfZJHSTvyYYWJbC9VbB47

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/room/lifecycle/NestViewModelFactory.kt

@@ -53,8 +53,12 @@ internal class NestViewModelFactory(
             // `httpClient` slot rather than as the first positional arg.
             httpClient = OkHttpNestsClient(httpClient = Amethyst.instance.roleBasedHttpClientBuilder::okHttpClientForVideo),
             transport = QuicWebTransportFactory(),
-            decoderFactory = { channelCount -> MediaCodecOpusDecoder(channelCount = channelCount) },
-            playerFactory = { channelCount -> AudioTrackPlayer(channelCount = channelCount) },
+            decoderFactory = { channelCount, sampleRate ->
+                MediaCodecOpusDecoder(channelCount = channelCount, sampleRate = sampleRate)
+            },
+            playerFactory = { channelCount, sampleRate ->
+                AudioTrackPlayer(channelCount = channelCount, sampleRate = sampleRate)
+            },
             signer = signer,
             room = room,
             captureFactory = { AudioRecordCapture() },