feat(nestsClient): MoQ ANNOUNCE family + Opus encoder + AudioRecord capture

Phase 4 (codec + audio capture slice). Adds the publisher-side MoQ
control messages and the Opus encode + microphone capture pieces a
speaker needs. The host-grants-speaker UI flow is deferred — that's
multi-screen UX that should be designed before being implemented.

commonMain (nestsclient.moq):
- 5 new MoqMessageType entries with codec round-trip + tests:
  * Announce (0x06): publisher offers a track namespace.
  * AnnounceOk (0x07): subscriber acknowledges.
  * AnnounceError (0x08): subscriber rejects with error code +
    reason phrase.
  * Unannounce (0x09): publisher withdraws a previously-announced
    namespace.
  * SubscribeDone (0x0B): publisher tells the subscriber no more
    objects are coming for this subscription, with stream count and
    reason.

commonMain (nestsclient.audio):
- New `OpusEncoder` interface — symmetric to `OpusDecoder`, one
  instance per outgoing track since Opus state is per-stream.
- New `AudioCapture` interface — `start()`, `readFrame()` returns a
  PCM frame or null when stopped, `stop()` releases the mic.

androidMain (nestsclient.audio):
- `MediaCodecOpusEncoder` — wraps `MediaCodec("audio/opus")` encoder
  variant (API 29+). 48 kHz mono in, 32 kbit/s VBR Opus out, 20 ms
  frames. Drains output queue per encode call.
- `AudioRecordCapture` — wraps `AudioRecord` from
  `MediaRecorder.AudioSource.VOICE_COMMUNICATION` so the platform's
  echo-cancellation + noise-suppression filters apply when available.
  Reads exactly one PCM frame per readFrame() call, retries on
  underrun, throws AudioException(DeviceUnavailable) on permission/
  resource failures.

commonTest:
- `AnnounceCodecTest` — 7 cases covering each message round-trip,
  concatenated decode in sequence, and a guard against accidentally
  reordering MoqMessageType enum codes.

Permission already declared:
- `RECORD_AUDIO` is already in amethyst/AndroidManifest.xml — no
  manifest change needed.

What this does NOT include:
- A publisher loop class (analogous to AudioRoomPlayer for publish
  direction) — can be added when the speak-button wiring lands.
- The host-grants-speaker UI — needs design input.
- STREAM_HEADER_SUBGROUP for stream-based object delivery — datagrams
  cover the listener happy-path; streams add reliability that nests
  may or may not require.

https://claude.ai/code/session_013nVLALALKaHVgHm9u5Cg8D

nestsClient/src/commonTest/kotlin/com/vitorpamplona/nestsclient/moq/AnnounceCodecTest.kt

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.nestsclient.moq
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertIs
+
+class AnnounceCodecTest {
+    @Test
+    fun announce_round_trip_with_parameters() {
+        val msg =
+            Announce(
+                namespace = TrackNamespace.of("nests", "test-room"),
+                parameters = listOf(SetupParameter(0x10L, byteArrayOf(0x01, 0x02))),
+            )
+        val decoded = MoqCodec.decode(MoqCodec.encode(msg))!!.message
+        assertEquals(msg, assertIs<Announce>(decoded))
+    }
+
+    @Test
+    fun announce_ok_round_trip() {
+        val msg = AnnounceOk(namespace = TrackNamespace.of("ns"))
+        val decoded = MoqCodec.decode(MoqCodec.encode(msg))!!.message
+        assertEquals(msg, assertIs<AnnounceOk>(decoded))
+    }
+
+    @Test
+    fun announce_error_round_trip() {
+        val msg =
+            AnnounceError(
+                namespace = TrackNamespace.of("nests", "denied-room"),
+                errorCode = 403,
+                reasonPhrase = "namespace already taken",
+            )
+        val decoded = MoqCodec.decode(MoqCodec.encode(msg))!!.message
+        assertEquals(msg, assertIs<AnnounceError>(decoded))
+    }
+
+    @Test
+    fun unannounce_round_trip() {
+        val msg = Unannounce(namespace = TrackNamespace.of("nests", "test-room"))
+        val decoded = MoqCodec.decode(MoqCodec.encode(msg))!!.message
+        assertEquals(msg, assertIs<Unannounce>(decoded))
+    }
+
+    @Test
+    fun subscribe_done_round_trip() {
+        val msg =
+            SubscribeDone(
+                subscribeId = 42,
+                statusCode = 0,
+                streamCount = 17,
+                reasonPhrase = "subscription expired",
+            )
+        val decoded = MoqCodec.decode(MoqCodec.encode(msg))!!.message
+        assertEquals(msg, assertIs<SubscribeDone>(decoded))
+    }
+
+    @Test
+    fun announce_then_announce_ok_decode_in_sequence() {
+        val ns = TrackNamespace.of("nests", "abc")
+        val ann = Announce(ns)
+        val ok = AnnounceOk(ns)
+        val bytes = MoqCodec.encode(ann) + MoqCodec.encode(ok)
+
+        val first = MoqCodec.decode(bytes, offset = 0)!!
+        val second = MoqCodec.decode(bytes, offset = first.bytesConsumed)!!
+
+        assertIs<Announce>(first.message)
+        assertIs<AnnounceOk>(second.message)
+        assertEquals(bytes.size, first.bytesConsumed + second.bytesConsumed)
+    }
+
+    @Test
+    fun every_publisher_message_type_has_a_known_code() {
+        // Guards against accidentally reordering MoqMessageType enum entries.
+        assertEquals(0x06L, MoqMessageType.Announce.code)
+        assertEquals(0x07L, MoqMessageType.AnnounceOk.code)
+        assertEquals(0x08L, MoqMessageType.AnnounceError.code)
+        assertEquals(0x09L, MoqMessageType.Unannounce.code)
+        assertEquals(0x0BL, MoqMessageType.SubscribeDone.code)
+    }
+}