chatgui: add shutdown diagnostics — ~DbManager, ~SoundManager, g_shutdown_sentinel

Three diagnostic points covering the gap between ~MainWindow done and CRT exit:
- DbManager: destroyed — confirms local dtors started after ~MainWindow
- SoundManager: static destructor entered — confirms static destruction phase
- main: static destructors done (g_shutdown_sentinel dtor) — confirms ALL statics done

If process hangs, we know exactly which phase failed.

tools/chatgui/db/db_manager.cpp

@@ -1,5 +1,6 @@
 #include "db_manager.h"
 #include "../src/debug_ui.h"
+#include "../../lib/debug_config.h"
 #include <openssl/sha.h>
 #include <openssl/evp.h>
 #include <cstring>
@@ -78,6 +79,7 @@ DbManager::~DbManager() {
     for (auto it = m_cursors.begin(); it != m_cursors.end(); ++it)
         sqlite3_finalize(it.value());
     m_cursors.clear();
+    DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "DbManager: destroyed");
 }
 
 sqlite3_stmt* DbManager::prepareOrNull(const char* sql) const {

tools/chatgui/src/main.cpp

@@ -10,6 +10,7 @@
 #include "../db/db_manager.h"
 #include "../transport/node_config.h"
 #include "../transport/utun_node.h"
+#include "../../lib/debug_config.h"
 
 #ifdef _WIN32
 static UtunNode* g_ctrl_node = nullptr;
@@ -23,6 +24,12 @@ static BOOL WINAPI console_ctrl_handler(DWORD dwCtrlType) {
 }
 #endif
 
+static struct ShutdownSentinel {
+    ~ShutdownSentinel() {
+        DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "main: static destructors done");
+    }
+} g_shutdown_sentinel;
+
 int main(int argc, char *argv[]) {
     QApplication app(argc, argv);
     app.setApplicationName("Chat");
@@ -98,6 +105,6 @@ int main(int argc, char *argv[]) {
 #endif
 
     int ret = app.exec();
-    qDebug("main: app.exec() returned %d", ret);
+    DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "main: app.exec() returned %d", ret);
     return ret;
 }

tools/chatgui/src/sound_manager.cpp

@@ -10,7 +10,10 @@ SoundManager* SoundManager::instance() {
     return &s;
 }
 
-SoundManager::~SoundManager() { shutdown(); }
+SoundManager::~SoundManager() {
+    DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "SoundManager: static destructor entered");
+    shutdown();
+}
 
 bool SoundManager::init() {
     if (m_initialized) return true;