M0: toolchain, monorepo scaffold, gateway plugin skeleton, CMP app

- gateway-plugin/: android platform plugin (plugin.yaml + adapter.py
  register(ctx) + no-op AndroidAdapter) + stub modules for M1-M5
- app/: Compose Multiplatform project (shared KMP + androidApp +
  desktopApp) with Gradle wrapper; builds :androidApp:assembleDebug
  and :desktopApp:compileKotlin
- scripts/guard_hermes_agent.sh + pre-commit hook: fail if hermes-agent/
  is staged (read-only reference, never committed)
- .gitignore excludes hermes-agent/; docs/ reference library

gateway-plugin/tests/README.md

@@ -0,0 +1,7 @@
+# Tests for the android gateway plugin.
+
+Run via hermes's hermetic runner (never bare pytest)::
+
+    scripts/run_tests.sh tests/gateway/test_android.py
+
+See ``docs/13-testing.md`` for the scenario list.