fix: preserve agent memory files when installing RA-H rules

- Add RA-H graph memory as a marked section instead of replacing files
- Make install-rules idempotent for AGENTS.md and CLAUDE.md
- Document the demo-safe memory file setup command

Generated with Claude Code

docs/8_mcp.md

@@ -133,6 +133,8 @@ Recommended guidance:
 Suggested memory-file snippet:
 
 ```md
+## RA-H Graph Memory
+
 You are helping build a thoughtful graph of atomic units of context.
 
 - Use `queryNodes` for direct lookup of a specific existing node.
@@ -141,3 +143,9 @@ You are helping build a thoughtful graph of atomic units of context.
 - `description` should state plainly what the thing is first, then why it belongs and current status.
 - Preserve the user's wording in `source` for user-authored ideas unless they explicitly want a rewrite.
 ```
+
+The installer can add or refresh this section without replacing the rest of the memory file:
+
+```bash
+npx -y ra-h-mcp-server@latest install-rules --client codex --target . --yes
+```