stcp: ed25519 pubkey exchange in handshake, fix instance destroy segfault, fix chat_tcp_test

- u_async.c: process immediate_queue BEFORE epoll_wait in uasync_poll
- stcp_link.c: defensive NULL etcp_conn/etcp_link in stcp_link_close
- utun_instance.c: move stcp_server_list_destroy_all to Phase J (before ETCP),
  add deferred drain in both Phase J and L
- stcp.h/c: STCP_HS_ENC_CLIENT 6→38, STCP_HS_ENC_SERVER 7→39,
  exchange ed25519_pubkey in both handshake directions
- etcp_connections.c: copy peer_ed25519 from STCP to ETCP_CONN in
  etcp_link_enter_ready_tcp; guard link->etcp in tcp_link_close_cb
- chat_sync.c: fix lk->conn NULL dereference for TCP links
- test_stcp.c: update stcp_server_create/stcp_client_connect callsites
- tools/chat_tcp_test: change transport udp→tcp

tools/chatgui/src/statuspage.cpp

@@ -0,0 +1,121 @@
+// statuspage.cpp — Status page (NTP + connections) in settings
+#include "statuspage.h"
+#include "../transport/utun_node.h"
+
+extern "C" {
+#include "../transport/gui_bridge.h"
+#include "chat/chat_core.h"
+}
+
+#include <QVBoxLayout>
+#include <QHBoxLayout>
+#include <QLabel>
+#include <QFont>
+#include <QTimer>
+#include <QDateTime>
+
+static StatusPage* g_activeStatusPage = nullptr;
+
+static void statusRefreshCallback(const char* text, int len) {
+    if (g_activeStatusPage)
+        g_activeStatusPage->setText(QString::fromUtf8(text, len));
+}
+
+StatusPage::StatusPage(UtunNode* node, QWidget* parent)
+    : QWidget(parent)
+    , m_node(node)
+{
+    auto* layout = new QVBoxLayout(this);
+    layout->setSpacing(2);
+    layout->setContentsMargins(0, 0, 0, 0);
+
+    /* ── clock block ── */
+    m_clockFrame = new QFrame(this);
+    m_clockFrame->setFrameStyle(QFrame::StyledPanel | QFrame::Sunken);
+    m_clockFrame->setStyleSheet(
+        "QFrame { border: 1px solid palette(mid); border-radius: 2px;"
+        " padding: 1px; background: palette(alternate-base); }");
+
+    auto* clockLayout = new QVBoxLayout(m_clockFrame);
+    clockLayout->setContentsMargins(4, 0, 4, 0);
+
+    m_clockLabel = new QLabel("--:--:--", m_clockFrame);
+    QFont clockFont("monospace", 20);
+    clockFont.setBold(true);
+    m_clockLabel->setFont(clockFont);
+    m_clockLabel->setAlignment(Qt::AlignCenter);
+    m_clockLabel->setStyleSheet("border: none; color: palette(text);");
+    clockLayout->addWidget(m_clockLabel);
+
+    layout->addWidget(m_clockFrame);
+
+    /* ── System Status section ── */
+    auto* title = new QLabel("System Status", this);
+    title->setStyleSheet("font-weight: bold; font-size: 13px;");
+    layout->addWidget(title);
+
+    m_textEdit = new QPlainTextEdit(this);
+    m_textEdit->setReadOnly(true);
+    m_textEdit->setFont(QFont("monospace", 10));
+    m_textEdit->setStyleSheet(
+        "QPlainTextEdit { border: 1px solid palette(mid); border-radius: 4px;"
+        " padding: 8px; background: palette(base); }");
+    m_textEdit->setPlaceholderText("Click Refresh to load status");
+    layout->addWidget(m_textEdit, 1);
+
+    auto* btnLayout = new QHBoxLayout();
+    btnLayout->addStretch();
+    m_refreshBtn = new QPushButton("Refresh", this);
+    m_refreshBtn->setFixedWidth(90);
+    m_refreshBtn->setStyleSheet(
+        "QPushButton { border: 1px solid palette(mid); border-radius: 4px;"
+        " padding: 6px 16px; font-size: 13px; background: palette(button); }"
+        "QPushButton:hover { background: palette(light); }");
+    connect(m_refreshBtn, &QPushButton::clicked, this, &StatusPage::onRefreshClicked);
+    btnLayout->addWidget(m_refreshBtn);
+    layout->addLayout(btnLayout);
+
+    m_clockTimer = new QTimer(this);
+    m_clockTimer->setSingleShot(true);
+    m_clockTimer->setTimerType(Qt::PreciseTimer);
+    connect(m_clockTimer, &QTimer::timeout, this, &StatusPage::updateClock);
+
+    g_activeStatusPage = this;
+    gui_bridge_set_status_refresh_cb(statusRefreshCallback);
+}
+
+StatusPage::~StatusPage() {
+    m_clockTimer->stop();
+    if (g_activeStatusPage == this) g_activeStatusPage = nullptr;
+}
+
+void StatusPage::updateClock() {
+    if (!m_node) return;
+
+    qint64 nowMs = QDateTime::currentMSecsSinceEpoch();
+    int64_t offsetUs = m_node->ntpOffsetUs();
+    bool synced = m_node->ntpSynced();
+
+    qint64 correctedMs = nowMs - (offsetUs / 1000);
+    QDateTime corrected = QDateTime::fromMSecsSinceEpoch(correctedMs).toLocalTime();
+
+    QString t = corrected.toString("HH:mm:ss");
+
+    if (synced)
+        m_clockLabel->setText(QString("%1  [NTP ✓]").arg(t));
+    else
+        m_clockLabel->setText(QString("%1  [LOCAL]").arg(t));
+
+    int msToNext = 1000 - (corrected.time().msec());
+    m_clockTimer->start(msToNext);
+}
+
+void StatusPage::refreshStatus() {
+    updateClock();
+    m_textEdit->setPlainText("Loading...");
+    gui_bridge_post_uasync_fn(chat_core_collect_status_trampoline, NULL);
+}
+
+void StatusPage::onRefreshClicked() {
+    refreshStatus();
+}