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/emojitabbar.cpp

@@ -0,0 +1,50 @@
+#include "emojitabbar.h"
+#include <QPainter>
+#include <QStyleOptionTab>
+
+EmojiTabBar::EmojiTabBar(QWidget *parent)
+    : QTabBar(parent)
+{
+    setDrawBase(false);
+    setExpanding(false);
+    setUsesScrollButtons(false);
+}
+
+void EmojiTabBar::paintEvent(QPaintEvent *event) {
+    Q_UNUSED(event);
+    QPainter p(this);
+    p.setRenderHint(QPainter::Antialiasing);
+
+    int w = width();
+    int h = height();
+    static const QColor bgColor(255, 255, 255);
+    static const QColor activeTextColor(0x33, 0x90, 0xEC);
+    static const QColor inactiveTextColor(0x8E, 0x8E, 0x93);
+    static const QColor activeBarColor(0x33, 0x90, 0xEC);
+    static const QColor separatorColor(0xE0, 0xE0, 0xE0);
+
+    p.fillRect(rect(), bgColor);
+
+    QFont f = font();
+    f.setPointSize(f.pointSize() - 1);
+    p.setFont(f);
+
+    int current = currentIndex();
+
+    for (int i = 0; i < count(); ++i) {
+        QRect r = tabRect(i);
+        if (!r.isValid()) continue;
+
+        bool active = (i == current);
+        p.setPen(active ? activeTextColor : inactiveTextColor);
+        p.drawText(r, Qt::AlignHCenter | Qt::AlignVCenter, tabText(i));
+
+        if (active) {
+            int barX = r.left() + 4;
+            int barW = r.width() - 8;
+            p.fillRect(QRect(barX, h - 3, barW, 3), activeBarColor);
+        }
+    }
+
+    p.fillRect(QRect(0, h - 1, w, 1), separatorColor);
+}