refactor: remove dead provides/consumes capability model

The program-level Capability model (provides/consumes) was a vestige of an
earlier design superseded by the deployment-level requires/Requirement graph.
It was read only into a diagnostic node and surfaced as an always-empty
'Capabilities' panel; nothing acted on it. Removed from manifest, relations,
the CLI re-export, and the System Map.

castle-api/tests/test_mqtt.py

@@ -1,110 +0,0 @@
-"""Tests for MQTT client serialization logic."""
-
-import json
-
-from castle_core.registry import Deployment, NodeConfig, NodeRegistry
-
-from castle_api.mqtt_client import _json_to_registry, _registry_to_json
-
-
-def _make_registry() -> NodeRegistry:
-    return NodeRegistry(
-        node=NodeConfig(
-            hostname="tower", castle_root="/data/repos/castle", gateway_port=9000
-        ),
-        deployed={
-            "my-svc": Deployment(
-                manager="systemd",
-                launcher="python",
-                run_cmd=["uv", "run", "my-svc"],
-                env={"PORT": "9001", "SECRET_KEY": "super-secret"},
-                description="My service",
-                name="my-svc",
-                kind="service",
-                stack="python-fastapi",
-                port=9001,
-                health_path="/health",
-                subdomain="my-svc",
-                managed=True,
-            ),
-            "my-job": Deployment(
-                manager="systemd",
-                launcher="command",
-                run_cmd=["my-job"],
-                name="my-job",
-                kind="job",
-                stack="python-cli",
-                schedule="0 2 * * *",
-            ),
-        },
-    )
-
-
-class TestRegistrySerialization:
-    """Round-trip serialization of NodeRegistry to/from JSON."""
-
-    def test_round_trip(self) -> None:
-        original = _make_registry()
-        json_str = _registry_to_json(original)
-        restored = _json_to_registry(json_str)
-
-        assert restored.node.hostname == "tower"
-        assert restored.node.gateway_port == 9000
-
-    def test_deployed_components_preserved(self) -> None:
-        original = _make_registry()
-        restored = _json_to_registry(_registry_to_json(original))
-
-        svc = restored.get("service", "my-svc")
-        assert svc is not None
-        assert svc.manager == "systemd"
-        assert svc.launcher == "python"
-        assert svc.port == 9001
-        assert svc.health_path == "/health"
-        assert svc.subdomain == "my-svc"
-        assert svc.managed is True
-        assert svc.kind == "service"
-        assert svc.stack == "python-fastapi"
-
-    def test_job_fields_preserved(self) -> None:
-        original = _make_registry()
-        restored = _json_to_registry(_registry_to_json(original))
-
-        job = restored.get("job", "my-job")
-        assert job is not None
-        assert job.launcher == "command"
-        assert job.schedule == "0 2 * * *"
-        assert job.kind == "job"
-        assert job.stack == "python-cli"
-
-    def test_optional_fields_omitted(self) -> None:
-        """Fields like port, health_path are None when not set."""
-        reg = NodeRegistry(
-            node=NodeConfig(hostname="minimal"),
-            deployed={
-                "bare": Deployment(
-                    manager="systemd", launcher="command", run_cmd=["bare"], name="bare"
-                ),
-            },
-        )
-        restored = _json_to_registry(_registry_to_json(reg))
-        bare = restored.get("service", "bare")
-        assert bare.port is None
-        assert bare.health_path is None
-        assert bare.subdomain is None
-        assert bare.schedule is None
-        assert bare.managed is False
-
-    def test_no_secrets_in_payload(self) -> None:
-        """env vars, run_cmd, and castle_root must not appear in MQTT payload."""
-        original = _make_registry()
-        json_str = _registry_to_json(original)
-        data = json.loads(json_str)
-
-        # No castle_root in node
-        assert "castle_root" not in data["node"]
-
-        # No env or run_cmd in any component
-        for name, comp in data["deployed"].items():
-            assert "env" not in comp, f"{name} has env in MQTT payload"
-            assert "run_cmd" not in comp, f"{name} has run_cmd in MQTT payload"