Add inventory creation workflow guidance to MCP instructions ...

- Document that docs must be created before inventory items referencing them
- Remind agents to always use MCP tools, never direct filesystem edits

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Describe MCP inventory write schema

Fix MCP usage parameter guidance

Improve MCP knowledge maintenance guidance

Document proactive MCP usage for agents

Add Gnexus Book MCP server