Add MCPProxy to Tools and code

[Dumbris]

Summary

• Adds MCPProxy to the Tools and code section (new entry on top per CONTRIBUTING.md)
• MCPProxy is an open-source MCP gateway with quarantine-based security, BM25 tool discovery, Docker isolation, and OAuth 2.1
• Relevant to MCP security as it provides quarantine-based security controls for MCP tool invocations