Add MCP server for tool dispatch and hc-run resource access

[binrogithub]

Motivation

• Provide a centralized MCP server to dispatch named tools including hc_tools_search, hc_run, hc_run_demo, and hc_doctor_fix and support admin-gated tools.
• Allow reading run artifacts and metadata via hc-run:// URIs backed by an abstract run store.
• Establish a new hc_agent package to host MCP server code.

Description

• Add McpServer class with fields run_store, tools, admin_tools, and policy, and provide a _missing_tool_stub for unconfigured tools.
• Implement list_tools() to enumerate available tools and call_tool(name, params, ctx) to dispatch to tools or admin_tools with policy gating and a structured error for unknown tools.
• Implement read_resource(uri) to parse hc-run://<run_id>/... URIs, fetch artifacts via run_store methods (read_artifact, get_artifact, open_artifact) or run info via get_run/read_run/run_info, and list_resources(prefix) to optionally list artifacts using run_store.list_artifacts.
• Add helper methods _parse_run_uri, _read_artifact, _read_run_info, _policy_allows_admin, and _format_run_resource, and create package initializers hc_agent/__init__.py and hc_agent/mcp/__init__.py.

Testing

• No automated tests were run on the modified code.

---

Codex Task