Investigate capability to validate the schema of MCPServers being registered with the Gateway

[maleck13]

Describe the bug
When a MCP server presents a tool with a bad schema agents cannot use the gateway

To Reproduce
Set up the gateway
connect claude
claude mcp add --transport http mcp-gateway http://mcp.127-0-0-1.sslip.io:8001/mcp

use the the gateway via a prompt

see

 API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.2.custom.input_schema: JSON schema is invalid. It must match JSON Schema draft 2020-12 (https://json-schema.org/draft/2020-12). Learn more about tool use at
     https://docs.claude.com/en/docs/tool-use."},"request_id":"req_vrtx_011CYzvzNNvyGRdfFJduQKWW"}

The issue is caused by the CustomResponse server we have for testing

[esnible]

The schema for tools is available at https://modelcontextprotocol.io/specification/2025-11-25/schema#tool

MCP Gateway should not hold/cache tools that don't conform to that schema.