chore(session): read .custodian-brief.md before MCP call in session init

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/rules/session-protocol.md

@@ -5,6 +5,12 @@ State Hub: http://127.0.0.1:8000
 ### Session Protocol
 
 **Step 1 — Orient**
+
+Read the offline-safe brief first:
+```bash
+cat .custodian-brief.md
+```
+Then call the MCP tool for richer context (skip if unreachable):
 ```
 get_domain_summary("custodian")
 ```