Enhance ComboHandler and orchestrator functionality with access control and error handling improvements

- Added AccessControl to ComboHandler for role-based access management.
- Implemented gas estimation for plan execution and improved gas limit checks.
- Updated execution and preparation methods to enforce step count limits and role restrictions.
- Enhanced error handling in orchestrator API endpoints with AppError for better validation feedback.
- Integrated request timeout middleware for improved request management.
- Updated Swagger documentation to reflect new API structure and parameters.

docs/CODE_REVIEW_CHECKLIST.md

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+# Code Review Checklist
+
+## Security
+- [ ] No hardcoded secrets or credentials
+- [ ] Input validation and sanitization
+- [ ] SQL injection prevention (parameterized queries)
+- [ ] XSS prevention
+- [ ] CSRF protection
+- [ ] Authentication/authorization checks
+- [ ] Rate limiting considerations
+- [ ] Error messages don't leak sensitive info
+
+## Code Quality
+- [ ] Code follows project style guide
+- [ ] Functions are single-purpose and well-named
+- [ ] No code duplication (DRY principle)
+- [ ] Proper error handling
+- [ ] Comments added for complex logic
+- [ ] No commented-out code (unless with explanation)
+
+## Testing
+- [ ] Unit tests added/updated
+- [ ] Integration tests added/updated (if applicable)
+- [ ] E2E tests added/updated (if applicable)
+- [ ] Tests pass locally
+- [ ] Edge cases covered
+
+## Performance
+- [ ] No N+1 queries
+- [ ] Database queries optimized
+- [ ] Caching used where appropriate
+- [ ] No unnecessary re-renders (React)
+- [ ] Large files handled efficiently
+
+## Documentation
+- [ ] JSDoc comments for public APIs
+- [ ] README updated if needed
+- [ ] API documentation updated
+- [ ] Breaking changes documented
+
+## Dependencies
+- [ ] New dependencies justified
+- [ ] Security vulnerabilities checked
+- [ ] Version updates safe
+
+---
+
+**Reviewer**: _____________  
+**Date**: _____________
+