fix(ws): drop upgrades arriving after closeWebSocket instead of crashing

closeWebSocket() nulls both WebSocketServer references but cannot unregister
the `server.on("upgrade")` listeners that initWebSocket/initPtyWebSocket
installed on the shared http.Server. An upgrade landing in that window threw

    TypeError: Cannot read properties of null (reading 'handleUpgrade')

from the listener — unhandled, so it killed the process mid-SIGTERM instead of
letting it exit gracefully, and no server came back up. Observed in
runtime/server.log right after a restart, with the dashboard then showing
"Mất kết nối" and nothing else.

The previous commit's TerminalView reconnect makes this near-certain rather
than rare: every open run console re-attaches to /ws-pty every 1.5s, so a
shutdown almost always has an upgrade in flight. Both listeners now destroy
the socket when their server is gone; clients retry, which is the correct
answer during a shutdown.

Regression test uses a real http.Server and raw upgrade requests — without the
guard the process dies and the test run hangs rather than reporting a failure.

server/__tests__/websocket-shutdown.test.js

@@ -0,0 +1,56 @@
+/**
+ * @file websocket-shutdown.test.js
+ * @description Regression test for the shutdown race in server/websocket.js:
+ * `closeWebSocket()` nulls both WebSocketServer references but cannot
+ * unregister the `server.on("upgrade")` listeners it installed, so an upgrade
+ * arriving mid-shutdown used to throw an unhandled TypeError
+ * ("Cannot read properties of null (reading 'handleUpgrade')") and kill the
+ * process. Uses a real http.Server and raw upgrade requests — no ws client.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+const { describe, it } = require("node:test");
+const assert = require("node:assert/strict");
+const http = require("node:http");
+const net = require("node:net");
+const ws = require("../websocket");
+
+/** Send a raw WS upgrade for `path` and resolve once the socket settles. */
+function rawUpgrade(port, path) {
+  return new Promise((resolve) => {
+    const socket = net.connect(port, "127.0.0.1", () => {
+      socket.write(
+        `GET ${path} HTTP/1.1\r\nHost: 127.0.0.1:${port}\r\n` +
+          `Upgrade: websocket\r\nConnection: Upgrade\r\n` +
+          `Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\nSec-WebSocket-Version: 13\r\n\r\n`
+      );
+    });
+    let body = "";
+    socket.on("data", (d) => {
+      body += d.toString("utf8");
+    });
+    socket.on("close", () => resolve(body));
+    socket.on("error", () => resolve(body));
+  });
+}
+
+describe("websocket shutdown race", () => {
+  it("drops upgrades that land after closeWebSocket instead of crashing", async () => {
+    const server = http.createServer((req, res) => res.end("ok"));
+    ws.initWebSocket(server);
+    ws.initPtyWebSocket(server);
+    await new Promise((r) => server.listen(0, "127.0.0.1", r));
+    const { port } = server.address();
+
+    // The shutdown the real server performs on SIGTERM.
+    ws.closeWebSocket();
+
+    // Both paths, because each has its own upgrade listener and its own null
+    // reference. An unguarded handleUpgrade here takes the process down, so
+    // simply reaching the assertions below is the test passing.
+    await rawUpgrade(port, "/ws");
+    await rawUpgrade(port, "/ws-pty/ccam-lane-1");
+
+    assert.equal(ws.getConnectionCount(), 0);
+    await new Promise((r) => server.close(r));
+  });
+});