test(mcp): add integration tests for MCP server (Part 5)

20 tests covering server initialization, tool listing, help tool,
auth guard, error translation, mock API tool calls, error scenarios
(404, 422, 429), and input validation. Uses MCP SDK InMemoryTransport
for end-to-end client-server testing.

https://claude.ai/code/session_01Y2eJZgKG78nDyN6Uw2tWQx

Author: claude