bundled: SIGTERM the frankenphp child via aboutToQuit, not just the dtor

Symptom (user report on v0.1.1):

  QProcess: Destroyed while process ("/tmp/.mount_Todo-xbNoHHL/usr/bin/frankenphp") is still running.

…and the frankenphp child + its PHP workers were left orphaned after
the host exited.

Cause: teardownChild() was only called from ~BackendConnection. By
the time that destructor runs, app.exec() has already returned,
QQmlApplicationEngine is mid-destruction, and Qt's event loop is
half-torn-down. waitForFinished() doesn't reliably reap the child in
that window — QProcess gets destroyed by the QObject parent-chain
cleanup before the kernel reports the child as exited.

Fix: in BackendConnection's constructor, connect
QCoreApplication::aboutToQuit → teardownChild. aboutToQuit fires
while the event loop is still active and BEFORE main() starts
unwinding the stack, so SIGTERM + waitForFinished can do their job
properly. The destructor's teardownChild call stays as belt-and-
suspenders (no-op once aboutToQuit has already cleaned up — the
function is idempotent via the m_child = nullptr at its end).

The connect happens unconditionally in the constructor (not just for
bundled mode) because m_child is also nullptr in dev mode and
teardownChild handles that with its leading `if (!m_child) return;`.

Regression guard: examples/todo/tests/bundled-supervisor.sh gains a
"graceful shutdown" step:

  - Snapshots the host's child PIDs before SIGTERM
  - SIGTERMs the host, waits up to 3s for clean exit
  - Greps the host log for "QProcess: Destroyed while" — fail if found
  - Iterates the snapshotted PIDs, fails on any frankenphp orphan still alive

Verified locally: real AppImage + the integration test both clean up
without Qt warnings or orphan processes.

PLAN.md: new v0.1.2 section above v0.1.1, this is its first entry.
CHANGELOG.md: [0.1.2] — TBD section with the same Fixed entry.

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

CHANGELOG.md

@@ -10,6 +10,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/)
 
 - (none yet — next changes land here)
 
+## [0.1.2] — TBD
+
+### Fixed
+
+- **Bundled supervisor: clean child shutdown.** `BackendConnection`'s destructor was the only path that called `teardownChild()`, but it ran during stack unwinding *after* `app.exec()` returned — by then the Qt event loop was already mid-shutdown and `QProcess::waitForFinished` couldn't reliably reap the child. Symptom: Qt logged `QProcess: Destroyed while process ("...frankenphp") is still running`, frankenphp + its PHP workers became orphans. The constructor now also connects `QCoreApplication::aboutToQuit` → `teardownChild`, so the child is SIGTERM'd while the event loop is still active. The bundled-supervisor integration test gained a clean-shutdown assertion (no Qt warning + no orphan frankenphp under the host's PGID after SIGTERM).
+
 ## [0.1.1] — 2026-05-03
 
 Bugfix release closing the four follow-ups identified during the v0.1.0 shakedown. No new public API surface; `/healthz` response gains an additive `bundle` field (existing JSON consumers ignore unknown keys).
@@ -62,6 +68,7 @@ First public preview. Phases 0 through 4a in PLAN.md are complete plus the Phase
 - The bundle ships without `composer.lock` (it's a library); the skeleton and the todo example carry their own.
 - Licensed under **LGPL-3.0-or-later** (`LICENSE` + `LICENSE.GPL` at the repo root). Chosen to align with Qt 6's LGPLv3 licensing — see PLAN.md §12 for the relinkability obligations the AppImage build already honours.
 
-[Unreleased]: https://src.bundespruefstelle.ch/magdev/php-qml/compare/v0.1.1...HEAD
+[Unreleased]: https://src.bundespruefstelle.ch/magdev/php-qml/compare/v0.1.2...HEAD
+[0.1.2]: https://src.bundespruefstelle.ch/magdev/php-qml/releases/tag/v0.1.2
 [0.1.1]: https://src.bundespruefstelle.ch/magdev/php-qml/releases/tag/v0.1.1
 [0.1.0]: https://src.bundespruefstelle.ch/magdev/php-qml/releases/tag/v0.1.0