chatgui: add sound playback via miniaudio (MP3 notification sounds)

- SoundManager singleton wraps ma_engine + ma_sound (non-blocking, background thread)
- MP3 files embedded in QRC, decoded to PCM at startup with MA_SOUND_FLAG_DECODE
- miniaudio.h (MIT) in lib/, IMPLEMENTATION in separate miniaudio_impl.c
- Sound settings page in SettingsDialog: enable/disable, volume slider (0-100%)
- Config keys [gui] sound_enabled, sound_volume
- Incoming messages trigger msg_incoming.mp3 sound

tools/chatgui/src/mainwindow.cpp

@@ -7,6 +7,7 @@
 #include "settingsdialog.h"
 #include "creategroupdialog.h"
 #include "invite_link.h"
+#include "sound_manager.h"
 #include "../db/db_manager.h"
 #include "../transport/utun_node.h"
 #include "../transport/gui_bridge.h"
@@ -18,6 +19,8 @@
 #include <QMessageBox>
 #include <QDebug>
 #include <QSettings>
+#include <QFile>
+#include <QTextStream>
 
 extern "C" {
 #include "../transport/chat_core.h"
@@ -80,6 +83,29 @@ MainWindow::MainWindow(QWidget *parent, DbManager* db, const QString& cfgPath,
     setupUi();
     setupTray();
 
+    SoundManager* sm = SoundManager::instance();
+    if (sm->init()) {
+        QFile cfgFile(m_cfgPath);
+        if (cfgFile.open(QIODevice::ReadOnly | QIODevice::Text)) {
+            bool inGui = false; bool enabled = true; int volume = 80;
+            QTextStream in(&cfgFile);
+            while (!in.atEnd()) {
+                QString line = in.readLine().trimmed();
+                if (line == "[gui]") { inGui = true; continue; }
+                if (line.startsWith("[") && line.endsWith("]")) inGui = false;
+                if (!inGui) continue;
+                if (line.startsWith("sound_enabled="))
+                    enabled = line.mid(15).trimmed() != "0";
+                else if (line.startsWith("sound_volume="))
+                    volume = line.mid(13).trimmed().toInt();
+            }
+            cfgFile.close();
+            sm->setEnabled(enabled);
+            sm->setVolume(volume / 100.0f);
+        }
+        sm->loadSound("msg_incoming", ":/sounds/msg_incoming.mp3");
+    }
+
     if (m_db) {
         s_mainWindow = this;
         gui_bridge_set_msg_received_cb(onMsgReceivedCallback);
@@ -277,6 +303,7 @@ void MainWindow::showSettings() {
 
 void MainWindow::onMessageReceived(const char* ch_id) {
     DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "MainWindow: msg received ch=%s", ch_id);
+    SoundManager::instance()->play("msg_incoming");
     if (m_messageList)
         m_messageList->refresh();
 }