* fix(mcp): sync required array with properties in tool schemas
MCP servers can emit schemas where the required array contains keys
not present in properties. This causes API 400 errors:
"Extra required key 'X' supplied."
- Add sanitizeSchemaRequired() to filter required arrays
- Apply it to MCP tool inputJSONSchema before sending to API
- Also fix filterSwarmFieldsFromSchema to update required after
removing properties
Fixes#525
* test: add MCP schema required sanitization test
