fix(desktop): dispose open PTY sessions in before-quit handler

The `before-quit` handler tears down the bootstrap controller, preview
watchers, and the Python backend but never disposes live PTY sessions.
When `app.quit()` proceeds to `FreeEnvironment()`, node-pty's
`ThreadSafeFunction::CallJS` callback fires on a half-torn-down
environment, throws a C++ exception that can no longer be caught, and
the process aborts (microsoft/node-pty#904).

Iterate `terminalSessions` and call `disposeTerminalSession()` (which
already calls `pty.kill()` + deletes the map entry) before killing the
backend, so the ThreadSafeFunctions are removed before teardown begins.

Closes #48335

apps/desktop/electron/main.cjs

@@ -6551,6 +6551,12 @@ app.on('before-quit', () => {
   flushDesktopLogBufferSync()
   closePreviewWatchers()
 
+  // Kill open PTYs before environment teardown to avoid the node-pty#904
+  // ThreadSafeFunction SIGABRT race.
+  for (const id of [...terminalSessions.keys()]) {
+    disposeTerminalSession(id)
+  }
+
   if (hermesProcess && !hermesProcess.killed) {
     hermesProcess.kill('SIGTERM')
   }