bundled: disconnect child signals before terminate() to prevent restart-during-shutdown

teardownChild called terminate() then waitForFinished(2000), then
disconnected the QProcess signals. But waitForFinished pumps a local
event loop — when frankenphp exited inside that wait, QProcess::finished
fired synchronously, ran onChildFinished as the crash-supervisor's
restart path, and spawned a brand-new frankenphp child during
shutdown. That child's QProcess was then destroyed mid-spawn during
stack unwinding, producing the "QProcess: Destroyed while process is
still running" warning the bundled-supervisor.sh test catches.

Fix: disconnect first, then terminate. Severing signals before the
wait turns terminate() into the synchronous reap it should always
have been; onChildFinished can't run for a process we're explicitly
tearing down.

Local integration test passes clean — both the cache-baked-mount-path
relaunch and the graceful-shutdown assertion go through without the
warning or any orphan frankenphp.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

framework/qml/src/BackendConnection.cpp

@@ -380,6 +380,14 @@ bool BackendConnection::spawnChild(QString* errorOut)
 void BackendConnection::teardownChild()
 {
     if (!m_child) return;
+    // Disconnect *before* terminating: waitForFinished() pumps a local event
+    // loop, so QProcess::finished would fire synchronously inside that wait,
+    // run onChildFinished as the crash-supervisor restart path, and spawn a
+    // brand-new frankenphp child during shutdown — the new QProcess then
+    // gets destroyed mid-spawn during stack unwinding and Qt warns
+    // "Destroyed while process is still running". Severing signals first
+    // turns terminate() into the synchronous reap it should always have been.
+    disconnect(m_child, nullptr, this, nullptr);
     if (m_child->state() != QProcess::NotRunning) {
         m_child->terminate();
         if (!m_child->waitForFinished(2000)) {
@@ -387,7 +395,6 @@ void BackendConnection::teardownChild()
             m_child->waitForFinished(1000);
         }
     }
-    disconnect(m_child, nullptr, this, nullptr);
     m_child->deleteLater();
     m_child = nullptr;
     m_childLogBuffer.clear();