Finish SAND-WP-0002: remote smoke, podman-compose, HTTP stub

- T10 smoke passed on CoulombCore (sand-boxer self-deploy, sandbox 4e542c51)
- Add e2e smoke compose, scripts/smoke-compose-e2e.sh, make smoke-remote
- Support SANDBOXER_COMPOSE_CMD for podman-compose hosts
- FastAPI v0 stub at sandboxer.api.app; migration gaps doc
- Mark workplan finished (all 10 tasks done)

e2e/e2e.yml

@@ -0,0 +1,8 @@
+# Smoke contract for sand-boxer self-deploy verification (SAND-WP-0002-T10).
+# Test execution semantics belong to wise-validator (SAND-WP-0003).
+name: sand-boxer
+compose_file: e2e/docker-compose.smoke.yml
+health_checks: []
+test_command: "true"
+timeout: 60
+cleanup: always