Implement GameCube/Wii audio playback via libansnd

Allocates an ansnd voice per stream and configures/starts it in
single-buffer mode (no continuous re-feed needed yet, matching the
PSP/Linux single-shot approach). Real linear panning from
directionality via left/right voice volume. ansnd has no polling API
for voice state, so finish detection uses a voice_callback (fired
from ansnd's own audio DMA interrupt, not the main thread) that sets
a flag audioStreamDolphinIsFinished() reads.

Links libansnd (new for this project) and wires duskdolphin/audio
into the CMake build for the first time.

Verified via the dusk-dolphin toolchain: both GameCube and Wii
targets compile and link cleanly. Runtime verification in headless
Dolphin was inconclusive - confirmed via an A/B test against a
pre-audio baseline build that a pre-existing MMIO flood (unrelated
to this change, reproduces identically with zero audio code present)
keeps the harness from reaching the game's own steady state before
timing out.

src/duskdolphin/audio/audiostreamdolphin.c

@@ -6,3 +6,94 @@
  */
 
 #include "audiostreamdolphin.h"
+#include "audio/audiostream.h"
+#include "assert/assert.h"
+#include "util/memory.h"
+#include <ansndlib.h>
+
+errorret_t audioStreamDolphinInit(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  const s32 voiceId = ansnd_allocate_voice();
+  if(voiceId < 0) {
+    errorThrow(
+      "Failed to allocate ansnd voice: %s", ansnd_get_error_string(voiceId)
+    );
+  }
+
+  stream->platform.voiceId = voiceId;
+  stream->platform.finished = false;
+
+  errorOk();
+}
+
+errorret_t audioStreamDolphinDispose(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  ansnd_deallocate_voice((u32) stream->platform.voiceId);
+
+  errorOk();
+}
+
+errorret_t audioStreamDolphinBuffer(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  const size_t frameSize = stream->pcm.channels * sizeof(int16_t);
+
+  // Simple linear pan; AUDIO_STREAM_LEFT/CENTER/RIGHT map to -128..0..127.
+  float_t pan = (float_t) stream->directionality / 128.0f;
+  if(pan < -1.0f) pan = -1.0f;
+  if(pan > 1.0f) pan = 1.0f;
+
+  const float_t baseVolume = (float_t) stream->volume / 255.0f;
+
+  stream->platform.finished = false;
+
+  ansnd_pcm_voice_config_t config;
+  memoryZero(&config, sizeof(ansnd_pcm_voice_config_t));
+  config.samplerate = stream->pcm.sampleRate;
+  config.format = ANSND_VOICE_PCM_FORMAT_SIGNED_16_PCM;
+  config.channels = stream->pcm.channels;
+  config.pitch = 1.0f;
+  config.left_volume = baseVolume * (pan > 0 ? (1.0f - pan) : 1.0f);
+  config.right_volume = baseVolume * (pan < 0 ? (1.0f + pan) : 1.0f);
+  config.frame_data_ptr = (u32) stream->data;
+  config.frame_count = (u32) (stream->dataSize / frameSize);
+  config.voice_callback = audioStreamDolphinVoiceCallback;
+  config.stream_callback = NULL; // single-buffer playback
+  config.user_pointer = stream;
+
+  s32 result = ansnd_configure_pcm_voice((u32) stream->platform.voiceId, &config);
+  if(result != ANSND_ERROR_OK) {
+    errorThrow(
+      "Failed to configure ansnd voice: %s", ansnd_get_error_string(result)
+    );
+  }
+
+  result = ansnd_start_voice((u32) stream->platform.voiceId);
+  if(result != ANSND_ERROR_OK) {
+    errorThrow(
+      "Failed to start ansnd voice: %s", ansnd_get_error_string(result)
+    );
+  }
+
+  errorOk();
+}
+
+bool_t audioStreamDolphinIsFinished(audiostream_t *stream) {
+  assertNotNull(stream, "Stream cannot be NULL.");
+
+  return stream->platform.finished;
+}
+
+void audioStreamDolphinVoiceCallback(void *userPointer, int32_t voiceState) {
+  audiostream_t *stream = (audiostream_t *) userPointer;
+
+  if(
+    voiceState == ANSND_VOICE_STATE_FINISHED ||
+    voiceState == ANSND_VOICE_STATE_STOPPED ||
+    voiceState == ANSND_VOICE_STATE_ERROR
+  ) {
+    stream->platform.finished = true;
+  }
+}