MCP server v2.21.0: Streamlined MCP document tools and feedback reporting

Improvements

give_feedback tool: The server instructions include a Feedback section, and unexpected tool errors point agents to the tool for reporting problems.

Removals

Document tools: Removed Markdown-specific document creation and patching tools, and renamed the JSON document tools to create_documents and edit_document.

migration_guide tool: Removed the tool now that migration guidance is provided as a separate sanity-migration agent skill (npx skills add sanity-io/agent-toolkit --skill sanity-migration).