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/ADRs/ADR-001-Architecture-Decisions.md

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+# ADR-001: Architecture Decisions
+
+## Status
+Accepted
+
+## Context
+ISO-20022 Combo Flow system requires decisions on architecture patterns, technology choices, and design principles.
+
+## Decisions
+
+### 1. Two-Phase Commit (2PC) Pattern
+**Decision**: Use 2PC for atomic execution across DLT and banking rails.
+
+**Rationale**:
+- Ensures atomicity across heterogeneous systems
+- Provides rollback capability
+- Industry standard for distributed transactions
+
+### 2. PostgreSQL for Persistence
+**Decision**: Use PostgreSQL as primary database.
+
+**Rationale**:
+- ACID compliance required for financial transactions
+- JSONB support for flexible plan storage
+- Strong ecosystem and tooling
+
+### 3. Redis for Caching
+**Decision**: Use Redis for caching and session management.
+
+**Rationale**:
+- High performance
+- Pub/sub support for real-time updates
+- Widely supported
+
+### 4. Smart Contract Architecture
+**Decision**: Separate handler, registry, and adapter contracts.
+
+**Rationale**:
+- Modularity and upgradeability
+- Security isolation
+- Easier testing and auditing
+
+### 5. Next.js for Frontend
+**Decision**: Use Next.js 14 with App Router.
+
+**Rationale**:
+- Server-side rendering for performance
+- Built-in API routes
+- Excellent developer experience
+
+---
+
+**Date**: 2025-01-15  
+**Author**: Engineering Team
+