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)

Makefile

@@ -1,6 +1,6 @@
 .DEFAULT_GOAL := help
 
-.PHONY: help setup install test lint format build check cli-version
+.PHONY: help setup install test lint format build check cli-version smoke-remote
 
 help: ## List available make targets
 	@awk 'BEGIN {FS = ":.*## "}; /^[a-zA-Z0-9_.-]+:.*## / {printf "  %-16s %s\n", $$1, $$2}' $(MAKEFILE_LIST)
@@ -26,4 +26,7 @@ build: ## Build wheel and sdist
 check: lint test ## Run lint and tests (CI gate)
 
 cli-version: ## Print CLI version (smoke test for entry point)
-	uv run sandboxer version
+	uv run sandboxer version
+
+smoke-remote: ## T10 remote create/destroy smoke (needs SANDBOXER_HOST)
+	./scripts/smoke-compose-e2e.sh