MCP: improvement guide, feedback tool, and propose_change confirmation

Updates to the MCP Server documentation and tools:

get_improvement_guide returns Ada’s entity improvement guide — when to use articles, coaching, playbooks, and other entities, plus best practices for making suggestions. Call it before using propose_change.

send_feedback lets AI assistants send structured feedback directly to Ada’s development team — for workflow gaps, tool quality issues, or missing capabilities.

propose_change now uses a three-phase flow: discover field schemas, preview the proposed change for user confirmation, then execute with confirmed: true.

Learn more in the MCP Server documentation.