add-fred-capability

Author a new Fred agent capability (manifest + tools/middleware) built on fred-sdk, execution-model-agnostic (ReAct and Graph agents). Picks the right authoring lane, maps each runtime need to tools() or a middleware hook, wires entry-point registration, and enforces the capability boundary (never hand-edit union/registry hotspots, no capability code in control-plane, no runtime info in LLM tool signatures).