Document coupon_nft.rs contract and complete coupon flow

[Josue19-08]

➡️ Title

Document coupon_nft.rs contract and complete coupon flow

📘 Description

Create comprehensive documentation explaining how the coupon NFT system works, including contract functions, emission process, redemption flow, and expiration handling. Provide clear examples and technical specifications for developers and stakeholders.

Context: Document the complete coupon system architecture and flow to help developers understand the implementation, troubleshoot issues, and maintain the system effectively.

✅ Acceptance Criteria

Contract documentation

• Create contracts/contracts/coupon-nft/README.md
• Document all contract functions with parameters and return values
• Explain contract storage structure and data keys
• Document events emitted by the contract
• Provide examples of contract function calls

Flow documentation

• Create src/docs/coupon-system-flow.md
• Document complete flow: token purchase → coupon emission → redemption
• Explain integration points between frontend, backend, and contract
• Document metadata generation and IPFS upload process
• Describe database relationships and data flow

API documentation

• Document /coupon/generate endpoint with request/response examples
• Document /coupon/redeem/:id endpoint with all possible responses
• Include error codes and troubleshooting guide
• Provide curl examples for testing endpoints
• Document authentication and authorization requirements

Technical specifications

• Explain coupon NFT structure and metadata schema
• Document expiration logic and validation rules
• Describe redemption validation process
• Explain contract security measures and limitations
• Document IPFS integration and fallback strategies

Architecture overview

• Create system architecture diagram showing all components
• Document data flow between components
• Explain contract deployment and initialization process
• Document environment setup and configuration
• Include troubleshooting section for common issues

Examples and use cases

• Provide complete code examples for contract interaction
• Document typical coupon lifecycle scenarios
• Include business partner integration examples
• Provide testing scenarios and expected outcomes
• Document edge cases and error handling

Maintenance and operations

• Document contract upgrade considerations
• Explain monitoring and logging requirements
• Document backup and recovery procedures
• Include performance considerations and limitations
• Provide operational runbooks for common tasks

⚠ Use kebab-case for all file and folder names.
⚠ Do not use default alias imports or relative paths like ../../components/foo.
⚠ Use alias paths with @, e.g. @/components/foo.
⚠ Structure the code with reusable components and reuse existing ones.

[JosueBrenes]

Hi, can i work in this issue? please