metrics: RTT/loss histograms + Ed25519 signing + peer exchange via INIT handshake + file logging to stats/<peer>.dat

- etcp_metrics struct: 12-bucket RTT histogram, 11-bucket loss histogram, 10-min snapshots (>=200 pkts)
- Total counters: packets/bytes sent/rcvd, losses (retrans + probe gap detection)
- CSV append to <stats_dir>/<peer_id>.dat every 10 min
- Ed25519 pubkey exchange in INIT handshake (V3), always present
- Signed metrics exchange via ETCP_SECTION_METRICS (0x0A)
- Received metrics saved as from_<peer_id>.dat with signature hex
- on_metrics_rcvd callback in ETCP_BINDINGS
- stats_dir derived from config file path, mkdir'd at instance init
- Simplified versioning: ETCP_INIT_REQ_SIZE / ETCP_INIT_RESP_SIZE via sizeof

tools/chatgui/src/main.cpp

@@ -1,9 +1,9 @@
 #include <QApplication>
-#include <QFile>
 #include <QDir>
-#include <QSettings>
 #include "mainwindow.h"
 #include "../db/db_manager.h"
+#include "../transport/node_config.h"
+#include "debug_ui.h"
 
 int main(int argc, char *argv[]) {
     QApplication app(argc, argv);
@@ -11,22 +11,39 @@ int main(int argc, char *argv[]) {
     app.setQuitOnLastWindowClosed(false);
 
     QString cfgPath = QCoreApplication::applicationDirPath() + "/chatgui.cfg";
-    QString dbPath  = "chats.db";
 
-    if (QFile::exists(cfgPath)) {
-        QSettings cfg(cfgPath, QSettings::IniFormat);
-        dbPath = cfg.value("db_path", "chats.db").toString();
+    NodeConfig cfg(cfgPath);
+    bool needSave = false;
+
+    if (!cfg.exists()) {
+        if (!cfg.create("chatgui", 1333)) {
+            qCritical("Failed to create config: %s", qPrintable(cfgPath));
+            return 1;
+        }
     } else {
-        QSettings cfg(cfgPath, QSettings::IniFormat);
-        cfg.setValue("db_path", "chats.db");
-        cfg.sync();
+        if (!cfg.load()) {
+            qCritical("Failed to load config: %s", qPrintable(cfgPath));
+            return 1;
+        }
+        if (cfg.privKey().length() != 64 || cfg.pubKey().length() != 64 ||
+            cfg.nodeId().length() != 16) {
+            cfg.generateIdentity();
+            needSave = true;
+        }
+        if (needSave)
+            cfg.save();
     }
 
+    if (!cfg.debugFile().isEmpty())
+        guiDebugFile(cfg.debugFile().toUtf8().constData());
+
+    QString dbPath = cfg.dbPath();
+    if (dbPath.isEmpty()) dbPath = "chats.db";
     if (!QDir::isAbsolutePath(dbPath))
         dbPath = QCoreApplication::applicationDirPath() + "/" + dbPath;
 
     DbManager db(dbPath);
-    MainWindow w(nullptr, &db);
+    MainWindow w(nullptr, &db, cfgPath, cfg.debugFile());
     w.show();
 
     return app.exec();