Notebook E2E in a macOS GraalVM native image (#191 milestone 1) #249

#191's first milestone (#242): the notebook E2E's 20 scenarios run inside a GraalVM native image on macOS. They draw PythonAppView offscreen into an ImageComposeScene, so no window and no AWT-free piece is needed. The binary must run on its own from its directory, with JAVA_HOME and PYTHONHOME unset and no libjvm.

Change, in python-multiplatform-compose/fixtures/notebook-e2e:

• Runner. NotebookE2eMain runs the 20 scenarios by explicit calls, with each class's @BeforeTest and no JUnit or reflection. It prints PASS/FAIL per scenario, then NOTEBOOK_E2E: n passed, m failed of 20, and exits non-zero on any failure. The wheel's site-packages and the app directory default to site-packages/ and app/ beside the executable.
• Tasks.
  • notebookE2eJvm: the runner on the JVM, the sanity check.
  • notebookE2eNativeAgent: the runner under native-image's tracing agent, writing the Compose/Skiko configuration into the module.
  • notebookE2eNativeCompile: native-image via the JDK 25 toolchain, with --no-fallback --enable-native-access=ALL-UNNAMED.
  • Staging beside the binary: stageNativeImagePythonHome (Desktop: find PYTHONHOME beside a native-image executable, and stage it there #246), the wheel and the app.
  • notebookE2eNativeRun: runs the binary with JAVA_HOME/PYTHONHOME removed, requires 20 passed, and checks otool -L for no libjvm.
• Then a macOS CI job.

Completion: notebookE2eNativeRun prints NOTEBOOK_E2E: 20 passed, 0 failed of 20 locally and on CI.