fix(ci): stop gradle daemon between flutter build apk and assembleAndroidTest (#554)

## Summary

The Firebase Test Lab job (issue #549) failed because `flutter build apk --debug --no-pub` spawned a Gradle daemon, whose journal-cache lock file was left on the persistent Dagger `gradle-cache` mount after the `WithExec` container was torn down. The next exec, `./gradlew --no-daemon app:assembleAndroidTest`, then timed out after 60s waiting for that stale lock:

```
> Timeout waiting to lock journal cache (/home/ci/.gradle/caches/journal-1). It is currently in use by another process.
  Owner PID: 88
  Our PID: 53
```

The pre-existing `--no-daemon` only prevented stale daemon-registry reuse, not stale lock files.

**Fix:** chain `./gradlew --stop` into the first `WithExec` so the daemon shuts down gracefully and releases its locks before Dagger snapshots the layer.

## Test plan

- [ ] CI passes
- [ ] Manually re-run the Firebase Tests workflow (`workflow_dispatch`) and confirm the Gradle journal-lock error no longer appears

Closes #549

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Till Düßmann (Claude agent) <tilldu@googlemail.com>
Reviewed-on: https://codeberg.org/guettli/sharedinbox/pulls/554

ci/main.go

@@ -814,7 +814,14 @@ func (m *Ci) DeployApk(
 // Returns a flat directory with app-debug.apk and app-debug-androidTest.apk.
 func (m *Ci) BuildAndroidDebugApks() *dagger.Directory {
 	built := m.firebaseBase().
-		WithExec([]string{"flutter", "build", "apk", "--debug", "--no-pub"}).
+		// `flutter build apk` spawns a Gradle daemon. When this WithExec ends the
+		// container is torn down and the daemon is killed, but its journal-cache
+		// lock file on the persistent gradle-cache volume keeps its dead PID — the
+		// next gradlew invocation then times out waiting for that lock. `gradlew
+		// --stop` shuts the daemon down gracefully so the lock is released before
+		// Dagger snapshots the layer.
+		WithExec([]string{"/bin/bash", "-c",
+			`flutter build apk --debug --no-pub && (cd android && ./gradlew --stop)`}).
 		WithWorkdir("/src/android").
 		// --no-daemon avoids connecting to a stale daemon whose registry file was
 		// preserved in the Dagger layer snapshot but whose process no longer exists.