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earlier design superseded by the deployment-level requires/Requirement graph.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.

cli/src/castle_cli/manifest.py

@@ -4,7 +4,6 @@ from castle_core.manifest import *  # noqa: F401, F403
 from castle_core.manifest import (  # noqa: F401 — explicit re-exports for type checkers
     BuildSpec,
     CaddyDeployment,
-    Capability,
     CommandsSpec,
     DefaultsSpec,
     DeploymentBase,