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/mainwindow.cpp

@@ -8,6 +8,7 @@
 #include "creategroupdialog.h"
 #include "invite_link.h"
 #include "sound_manager.h"
+#include "audiorecorder.h"
 #include "animtimer.h"
 #include "../db/db_manager.h"
 #include "../transport/utun_node.h"
@@ -70,6 +71,7 @@ MainWindow::MainWindow(QWidget *parent, DbManager* db, const QString& cfgPath,
     , m_db(db), m_cfgPath(cfgPath), m_cfgDbPath(dbPath)
     , m_cfgDebugFile(debugFile), m_cfgDebugLevel(debugLevel)
     , m_cfgDebugCategories(debugCategories)
+    , m_recorder(nullptr)
 {
     setWindowTitle("Chat");
     resize(900, 600);
@@ -85,6 +87,7 @@ MainWindow::MainWindow(QWidget *parent, DbManager* db, const QString& cfgPath,
 }
 
 MainWindow::~MainWindow() {
+    if (m_recorder) { m_recorder->shutdown(); m_recorder = nullptr; }
     SoundManager::instance()->shutdown();
     DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "MainWindow: ~MainWindow — saving channel state");
     if (m_messageList) m_messageList->saveChannelState();
@@ -101,7 +104,8 @@ void MainWindow::setupUi() {
     auto *splitter = new QSplitter(Qt::Horizontal, this);
 
     m_channelList = new ChannelList(m_db, splitter);
-    m_messageList = new MessageList(m_db, splitter);
+    m_recorder = new AudioRecorder(this);
+    m_messageList = new MessageList(m_db, m_recorder, splitter);
     m_accountList = new AccountList(m_db, splitter);
 
     splitter->addWidget(m_channelList);
@@ -195,6 +199,14 @@ void MainWindow::setupSoundFromConfig() {
                          m_db->getUiStateInt(QStringLiteral("sound_%1_vol").arg(ek), 80) / 100.0f);
         }
     }
+
+    if (m_recorder) {
+        m_recorder->init();
+        if (m_db && m_db->isOpen())
+            m_recorder->setCaptureDeviceIndex(m_db->getUiStateInt("audio_input_device", -1));
+        qDebug("MainWindow: AudioRecorder initialized (captureDevice=%d)",
+               m_recorder->captureDeviceIndex());
+    }
 }
 
 void MainWindow::setupBridgeCallbacks() {