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/API_DEPRECATION_POLICY.md

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+# API Deprecation Policy
+
+## Overview
+This document outlines the deprecation policy for the ISO-20022 Combo Flow Orchestrator API.
+
+## Deprecation Timeline
+
+1. **Announcement**: Deprecated endpoints will be announced 6 months before removal
+2. **Warning Period**: Deprecation warnings in headers for 3 months
+3. **Sunset Date**: Full removal after 6 months
+
+## Deprecation Process
+
+### Phase 1: Announcement (Month 1-6)
+- Add deprecation notice to API documentation
+- Include deprecation headers in API responses
+- Notify all API consumers
+
+### Phase 2: Warning Period (Month 4-6)
+- Continue serving deprecated endpoints
+- Add migration guides
+- Provide alternative endpoints
+
+### Phase 3: Sunset (Month 7+)
+- Remove deprecated endpoints
+- Return 410 Gone status for removed endpoints
+
+## Migration Guides
+
+### From v1 to v2
+- [Migration guide for v1 → v2](./MIGRATION_V1_V2.md)
+
+---
+
+**Last Updated**: 2025-01-15
+