docs(vdb): repoint harness MCP registration + routing at vdb
Step 6, harness slice. Builds on !13 (merged).
All five docs/harnesses/*.md now register the MCP server as vdb serve --vault /path/to/your/vault (standalone python3 …/vault-mcp-server.py kept as an inline note), and their model-routing / reindex examples use vdb agents / vdb models / vdb index. The one genuine source-file reference (scripts/generate-agents.py's make_pi_agent) stays a path.
Docs-only.