chatgui: per-event sound settings with DB persistence

- Sound files loaded from filesystem (sound_dir in INI config, absolute or relative)
- Per-event enable/disable + volume stored in DB (ui_state table)
- SoundManager: setEvent(), effective volume = master * per-event
- SoundSettingsPage UI: 4 event rows (checkbox + slider)
- chat_core_save_ui_state() for async DB writes via uasync thread
- DbManager::getUiStateInt() for reading settings from GUI thread
- Default sounds copied to sounds/ dir next to DB, config entries written

tools/chatgui/db/db_manager.cpp

@@ -363,6 +363,14 @@ QString DbManager::getUiState(const QString& key) const {
     return val;
 }
 
+int DbManager::getUiStateInt(const QString& key, int defaultVal) const {
+    QString val = getUiState(key);
+    if (val.isEmpty()) return defaultVal;
+    bool ok = false;
+    int v = val.toInt(&ok);
+    return ok ? v : defaultVal;
+}
+
 /* ── sync operations (read-only, for gui_bridge) ── */
 
 QByteArray DbManager::syncListChannels() const {