server: cloned voice registry over the OpenAI surface

POST /v1/voices registers a voice from a WAV extracted server side
through qt_extract_voice_ref or from pre extracted .spk and .rvq
latents taken verbatim, DELETE drops it and GET lists it alongside the
model speakers. A registered voice wins over a speaker of the same
name and injects the reference latents into qt_tts_params, ref_text
present selects ICL clone mode. The registry lives in process RAM
under the synthesis mutex, so registration and lookups never race a
running synthesis. The audio and rvq readers gain buffer variants
factored from the file paths. The README and the architecture
document catch up on the streaming decode, the hidden bridge, and the
server endpoints.

src/audio-io.h

@@ -96,17 +96,10 @@ static float * audio_read(const char * path, int * T_out, int * sr_out) {
     return result;
 }
 
-// Read WAV, resample to target_sr, downmix to mono.
-// Returns a flat buffer of T floats at target_sr mono. Caller frees.
-static float * audio_read_mono(const char * path, int target_sr, int * T_out) {
-    int     T   = 0;
-    int     sr  = 0;
-    float * raw = audio_read(path, &T, &sr);
-    if (!raw) {
-        *T_out = 0;
-        return NULL;
-    }
-
+// Resample a planar stereo buffer to target_sr and downmix to mono.
+// Consumes raw (freed on every path). Returns a flat buffer of T floats,
+// caller frees.
+static float * audio_mono_from_planar(float * raw, int T, int sr, int target_sr, int * T_out) {
     // Resample planar stereo to target_sr first to keep both channels
     // coherent when the source rate differs.
     float * stereo_rs = raw;
@@ -144,6 +137,31 @@ static float * audio_read_mono(const char * path, int target_sr, int * T_out) {
     return mono;
 }
 
+// Read WAV, resample to target_sr, downmix to mono.
+// Returns a flat buffer of T floats at target_sr mono. Caller frees.
+static float * audio_read_mono(const char * path, int target_sr, int * T_out) {
+    int     T   = 0;
+    int     sr  = 0;
+    float * raw = audio_read(path, &T, &sr);
+    if (!raw) {
+        *T_out = 0;
+        return NULL;
+    }
+    return audio_mono_from_planar(raw, T, sr, target_sr, T_out);
+}
+
+// Same conversion from an in-memory WAV byte buffer.
+static float * audio_read_mono_buf(const uint8_t * data, size_t size, int target_sr, int * T_out) {
+    int     T   = 0;
+    int     sr  = 0;
+    float * raw = audio_io_read_wav_buf(data, size, &T, &sr);
+    if (!raw) {
+        *T_out = 0;
+        return NULL;
+    }
+    return audio_mono_from_planar(raw, T, sr, target_sr, T_out);
+}
+
 // WAV output format
 enum WavFormat {
     WAV_S16,  // 16-bit signed integer PCM (classic RIFF, default)