A node holds its link open, and applies what the mesh signs

The loop the whole thing exists for: told, apply, report.

`run` holds one outbound connection open and consumes the node's own queue.
Every declaration is verified against the control plane's signing key before a
byte of it is read as an instruction -- not once at connect, every time. The
transport being pinned is a different question from the instruction being
genuine, and pinning only the first would make the second transitive: a
compromised broker could forge declarations, and this host applies whatever the
link delivers.

Malformed and forged are reported differently, because ADR 0004 requires a host
to tell "this is not from the mesh I joined" from "this is broken". One means
somebody is trying and the other means something needs fixing.

A node now keeps what it needs to come back on its own: the broker's address
and fingerprint, the signing key it believes, and its own broker password --
which the mesh issues at enrolment to replace the token's secret, so the
one-time thing stays one-time and the credential it holds for years is not the
one that was pasted into a terminal.

Verified in the lab end to end. The node enrolled, held its link, received a
signed declaration and applied it -- the file is on the machine with the right
contents, and the host's own record lists both resources.

That run also found issue 010, which is recorded in novox/hq: the declaration
removed every container on the machine, including the control plane that sent
it. Correct reconciliation, shared store, and the first thing that happens.

examples/substrate-first-node.lock

@@ -74,7 +74,7 @@
       "command": ["docker", "run", "--rm", "--network", "container:mesh-store",
                   "-e", "MESH_STORE_INVENTORY=postgres://postgres:bootstrap@127.0.0.1:5432/inventory?sslmode=disable",
                   "-e", "MESH_STORE_IDENTITY=postgres://postgres:bootstrap@127.0.0.1:5432/identity?sslmode=disable",
-                  "192.0.2.250:5000/mesh-control@sha256:c6e96dc574ea52085bae4ed0a64e593ee512265ecb226643aa1fcbaf56d78396",
+                  "192.0.2.250:5000/mesh-control@sha256:1dfcf6a879e16e671d4d6459271fd2630e30560afa1211508ab3994494786893",
                   "migrate"],
       "verify": ["sh", "-c", "docker exec mesh-store psql -U postgres -d inventory -tAc \"select to_regclass('public.node')\" | grep -qx node && docker exec mesh-store psql -U postgres -d identity -tAc \"select to_regclass('public.signing_key')\" | grep -qx signing_key"]
     },
@@ -108,7 +108,7 @@
       "id": "control-plane",
       "type": "container",
       "name": "mesh-control",
-      "image": "192.0.2.250:5000/mesh-control@sha256:c6e96dc574ea52085bae4ed0a64e593ee512265ecb226643aa1fcbaf56d78396",
+      "image": "192.0.2.250:5000/mesh-control@sha256:1dfcf6a879e16e671d4d6459271fd2630e30560afa1211508ab3994494786893",
       "network": "host",
       "args": ["serve"],
       "volumes": ["mesh-broker-tls:/broker-tls:ro"],