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)

src/sandboxer/core/manager.py

@@ -48,6 +48,7 @@ class SandboxManager:
             status.sandbox_id = handle["sandbox_id"]
             status.inputs["compose_file"] = handle.get("compose_file", "")
             status.inputs["ssh_user"] = handle.get("ssh_user", "")
+            status.inputs["compose_cmd"] = handle.get("compose_cmd", "")
             reach = backend.wait_ready(handle)
             status.reachability = Reachability(**reach)
             status.state = SandboxState.READY
@@ -98,6 +99,7 @@ class SandboxManager:
             "compose_project": status.reachability.compose_project if status.reachability else "",
             "compose_file": status.inputs.get("compose_file", ""),
             "ssh_user": status.inputs.get("ssh_user", ""),
+            "compose_cmd": status.inputs.get("compose_cmd", ""),
         }
         backend.teardown(handle)