feat(mesh): cross-node routing + presence breaker (Phase 3)

- NodeConfig.address: routable host peers proxy to (wired registry + wire)
- compute_routes emits 'remote' routes for consumed peer services
  (local requires ref satisfied by an online peer -> <address>:<port>)
- _host_remote_block: fail-fast reverse_proxy (2s dial, passive health);
  presence expiry removes the route entirely = the primary circuit-breaker
- mesh_gateway.py: API re-renders + reloads the Caddyfile on mesh change,
  iff content changed (no-op until a cross-node service is consumed)
- tests: route emit / address fallback / breaker-absent / unconsumed

Logic verified hermetically + against primer's real registry (castle-api ->
primer:9020); live integration proven a no-op on civil.

castle-api/src/castle_api/mesh_wire.py

@@ -28,6 +28,8 @@ def registry_to_json(registry: NodeRegistry) -> str:
             "gateway_domain": registry.node.gateway_domain,
             # fleet role — so peers know which node is the config/secret authority.
             "role": registry.node.role,
+            # routable host peers proxy to for this node's services.
+            "address": registry.node.address,
         },
         "deployed": {},
     }
@@ -76,6 +78,7 @@ def json_to_registry(payload: str) -> NodeRegistry:
         gateway_port=node_data.get("gateway_port", 9000),
         gateway_domain=node_data.get("gateway_domain"),
         role=node_data.get("role", "follower"),
+        address=node_data.get("address"),
     )
     deployed: dict[str, Deployment] = {}
     for key, comp_data in data.get("deployed", {}).items():