fix(swarm): mTLS client-cert authz on the swarm control plane

The swarm controller (port 8770) exposed 9 routes with zero app-layer
auth, and swarmctl --tls defaulted off — anyone able to reach the port
could enroll workers (minting CA-signed certs + private keys), deploy,
or tear down the fleet. Two fail-closed layers:

- require_operator_cert gates every operator route (enroll/deploy/
  teardown/hosts/check/deckies). When mTLS is on, the peer cert's CN
  must be an operator identity (decnet-master/swarmctl); worker and
  updater@* certs are rejected. Plaintext loopback (single-host master)
  is accepted as the local operator — the docker.sock boundary.
- swarmctl refuses to bind a routable interface without --tls, so a
  network-exposed plaintext control plane can never start.

/heartbeat keeps its worker fingerprint pinning. Closes the two ASVS
criticals (control-plane no-auth, unauthenticated cert minting).

tests/swarm/test_heartbeat_lifecycle.py

@@ -47,7 +47,8 @@ def client(repo, ca_dir: pathlib.Path):
     async def _override() -> Any:
         return repo
     app.dependency_overrides[get_repo] = _override
-    with TestClient(app) as c:
+    # loopback client so operator-gated /swarm/enroll accepts the local operator.
+    with TestClient(app, client=("127.0.0.1", 50000)) as c:
         yield c
     app.dependency_overrides.clear()