Add hc_agent MCP gateway and server exposing hc_tools endpoints

[binrogithub]

Motivation

• Provide an MCP-facing module to surface higher-level hc_agent tooling via a stable programmatic interface.
• Centralize tool discovery and routing through a shared gateway layer so callers can reliably list and invoke tools.

Description

• Add package hc_agent with hc_agent.mcp exports and a thin server façade in hc_agent/mcp/server.py exposing HCMCPServer, hc_tools_search, hc_run, hc_run_demo, hc_doctor_fix, and list_tools.
• Implement a gateway in hc_agent/mcp/gateway.py that defines ToolSpec, a stable _TOOL_SPECS registry, serializable list_tools()/list_tool_specs() helpers, and call_tool() routing to per-tool handlers.
• Register and implement handlers for hc_tools_search, hc_run, hc_run_demo, and hc_doctor_fix with simple input validation and consistent response shapes.
• Export the new API from hc_agent/mcp/__init__.py so callers can import the server and functions directly.

Testing

• No automated tests were executed for these changes; no test failures were observed because tests were not run.

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Codex Task