feat: integrate Opus codec into lib/libopus + voice messages in chatgui

- Add lib/libopus/ (opus v1.6.1 embedded source: CELT 18 .c, SILK 77 .c, SILK float 28 .c, OPUS core 14 .c)
- Add lib/opus_codec.h/.c (wrapper: encoder, decoder, raw PCM int16)
- Add tests/test_opus_codec.c (7 tests: silence, sine, compression, PLC, null, defaults, multi-frame)
- chatgui: AudioRecorder (miniaudio capture, 48kHz mono)
- chatgui: VoiceEncoder (PCM→Opus file with custom container)
- chatgui: VoicePlayer (Opus→PCM playback via SoundManager)
- chatgui: PTT button in InputBar, voice message send/receive in MessageList
- chatgui: AudioDeviceSettingsPage (device selection, persisted in ui_state)
- chatgui: MessageDelegate voice message rendering (play button + duration)
- Update autotools: configure.ac, Makefile.am, src/Makefile.am, tests/Makefile.am
- Update CMake: chatgui CMakeLists.txt, libutun CMakeLists.txt (link libopus_internal.a)

tools/chatgui/src/audiodevicesettingspage.cpp

@@ -0,0 +1,95 @@
+#include "audiodevicesettingspage.h"
+#include "sound_manager.h"
+#include "../db/db_manager.h"
+#include "../transport/gui_bridge.h"
+#include "../../lib/mem.h"
+extern "C" {
+#include "../transport/chat_core.h"
+}
+#include <QVBoxLayout>
+#include <QLabel>
+#include <QFormLayout>
+#include <QDebug>
+
+AudioDeviceSettingsPage::AudioDeviceSettingsPage(DbManager* db, QWidget* parent)
+    : QWidget(parent), m_db(db)
+{
+    auto* layout = new QVBoxLayout(this);
+    layout->setContentsMargins(0, 12, 0, 0);
+
+    auto* infoLabel = new QLabel("Select audio devices for playback and recording.\nChanges take effect after restart.", this);
+    infoLabel->setWordWrap(true);
+    infoLabel->setStyleSheet("color: palette(text); font-size: 12px;");
+    layout->addWidget(infoLabel);
+
+    auto* formLayout = new QFormLayout();
+    formLayout->setContentsMargins(0, 16, 0, 0);
+    formLayout->setSpacing(10);
+
+    auto* outLabel = new QLabel("Playback device:", this);
+    m_outputCombo = new QComboBox(this);
+    m_outputCombo->setStyleSheet(
+        "QComboBox { border: 1px solid palette(mid); border-radius: 4px;"
+        " padding: 6px 10px; font-size: 13px; background: palette(base); }");
+    formLayout->addRow(outLabel, m_outputCombo);
+
+    auto* inLabel = new QLabel("Recording device:", this);
+    m_inputCombo = new QComboBox(this);
+    m_inputCombo->setStyleSheet(m_outputCombo->styleSheet());
+    formLayout->addRow(inLabel, m_inputCombo);
+
+    layout->addLayout(formLayout);
+    layout->addStretch();
+}
+
+void AudioDeviceSettingsPage::loadFromDb() {
+    auto playbackDevs = SoundManager::enumeratePlaybackDevices();
+    auto captureDevs = SoundManager::enumerateCaptureDevices();
+
+    m_outputCombo->clear();
+    for (int i = 0; i < playbackDevs.size(); i++) {
+        QString label = playbackDevs[i].name;
+        if (playbackDevs[i].isDefault) label += " (default)";
+        m_outputCombo->addItem(label, i);
+        if (playbackDevs[i].isDefault && m_savedOutputIdx < 0) m_savedOutputIdx = i;
+    }
+
+    m_inputCombo->clear();
+    for (int i = 0; i < captureDevs.size(); i++) {
+        QString label = captureDevs[i].name;
+        if (captureDevs[i].isDefault) label += " (default)";
+        m_inputCombo->addItem(label, i);
+        if (captureDevs[i].isDefault && m_savedInputIdx < 0) m_savedInputIdx = i;
+    }
+
+    if (m_db) {
+        m_savedOutputIdx = m_db->getUiStateInt("audio_output_device", m_savedOutputIdx);
+        m_savedInputIdx  = m_db->getUiStateInt("audio_input_device", m_savedInputIdx);
+    }
+
+    if (m_savedOutputIdx >= 0 && m_savedOutputIdx < m_outputCombo->count())
+        m_outputCombo->setCurrentIndex(m_savedOutputIdx);
+    if (m_savedInputIdx >= 0 && m_savedInputIdx < m_inputCombo->count())
+        m_inputCombo->setCurrentIndex(m_savedInputIdx);
+}
+
+void AudioDeviceSettingsPage::applyAndSave() {
+    int outIdx = m_outputCombo->currentData().toInt();
+    int inIdx  = m_inputCombo->currentData().toInt();
+
+    auto saveKey = [](const char* key, int val) {
+        QByteArray v = QByteArray::number(val);
+        size_t klen = strlen(key), vlen = (size_t)v.size();
+        size_t total = klen + 1 + vlen + 1;
+        void* arg = u_malloc(total);
+        memcpy(arg, key, klen + 1);
+        memcpy((char*)arg + klen + 1, v.constData(), vlen + 1);
+        gui_bridge_post_uasync_fn(chat_core_save_ui_state_trampoline, arg);
+    };
+    saveKey("audio_output_device", outIdx);
+    saveKey("audio_input_device", inIdx);
+
+    m_savedOutputIdx = outIdx;
+    m_savedInputIdx  = inIdx;
+    qDebug("AudioDeviceSettings: saved output=%d input=%d", outIdx, inIdx);
+}