Sub-issue of #56 (G2 of TechDevGroup/devagentic#203).

Scope

• read_artifact(artifact_id) MCP tool — wraps devagentic's artifact read surface
• patch_artifact(artifact_id, patch_body) MCP tool — wraps devagentic's in-place artifact edit

Acceptance

• Both tools registered under mcp_serve.py::_register_devagentic_mutation_tools.
• Unit tests covering happy path + error paths.
• Identify exact devagentic resolver names (search api.py for read_artifact / patch_artifact / similar).