MCP create_request schema uses member_id but API requires created_by_member_id

The create_request tool schema advertises member_id and external_user_id as the author fields. Neither is honored. The API only accepts created_by_member_id or created_by_external_user_id, which aren't in the schema.

Steps to reproduce: call create_request with a valid member_id, or with external_user_id, for an existing member.

Result: HTTP 400 "Provide created_by_member_id or created_by_external_user_id for an existing member."

Expected: the request is created with that member as its creator.

Impact: agents and clients that follow the schema can't create requests at all, because the author is required and no documented field works. It only succeeds by passing an undocumented field.

Suggested fix:

- Either map member_id/external_user_id to the created_by_* fields, or rename the schema fields to match the API.

- Mark the author as required in the schema.

- Also, status_id appears to be required (omitting it returns a bare "Required" error), but the schema doesn't mark it as required. Mark it required, or default to Pending.

- Update the README and docs for @project-echo/mcp.