Pin mcp<2 to avoid fastmcp import breakage ...

mcp 2.0.0 removed mcp.server.fastmcp, breaking the import in
mcp_protocol.py at startup and causing uvicorn to crash (502 on all
pages after a clean image rebuild). Pin to >=1.27.1,<2 so the resolved
mcp 1.27.1 keeps the working FastMCP API.

Co-Authored-By: Claude <noreply@anthropic.com>

Add official MCP transport and production hardening

Implement initial gnexus-creds MVP scaffold