Add: code.md with efficiency guide + summary instructions

✅ Created code.md - Comprehensive guide on:
- OpenHands sub-agents (File Editor, Bash Runner, Search, Code Analyzer)
- Cost optimization strategies (token budgets, structured tasks)
- Time reduction techniques (parallel execution, incremental builds)
- Best practices for Phase 3 (task granularity, error handling)
- Performance targets (< 60s build, < /bin/bash.10 cost)
- Troubleshooting sub-agent issues

✅ Updated CLAUDE.md:
- Added summary instructions section
- Referenced code.md in documentation section

Benefits:
- Clear guidance for efficient Phase 3 development
- Cost reduction strategies documented
- Sub-agent usage best practices
- Performance targets set
- Ready for implementation

CLAUDE.md

@@ -75,6 +75,7 @@ Used for: SSH authentication from n8n to localhost
 - **Phase 2 Details:** `phase2.md`
 - **Phase 3 Plan:** `phase3.md`
 - **n8n API Reference:** `n8n-api.md`
+- **Code Efficiency & Sub-Agents:** `code.md`
 - **Data Preservation Solution:** `N8N_DATA_PRESERVATION_SOLUTION.md`
 - **Gitea Webhook Setup:** `GITEA_N8N_WEBHOOK_GUIDE.md`
 - **Test Scripts:** `test-scripts/README.md`