feat(backend): Multi-Modal Produce Shelf-Life & Spoilage Decay API

[hrshjswniii]

📌 Overview

This PR implements [feature] : Multi-Modal Produce Shelf-Life & Spoilage Decay API combining IoT thermal degree-hours via Arrhenius kinetic decay equation ($k = A \cdot e^{-E_a / (R \cdot T)}$), computer vision spot/necrosis ratios, and humidity respiration penalties to calculate real-time remaining shelf-life days and produce decay index percentages (0-100%).

Key Changes Introduced:

1. Multi-Modal Spoilage Engine:
   • Updated [backend/services/spoilageDetectionService.js]implementing calculateMultiModalShelfLife(params).
2. Backend API Endpoint:
   • Updated [backend/routes/aiRoutes.js] with POST /api/ai/predict-shelflife.
3. Automated Unit Test Suite:
   • Created [backend/tests/spoilageDecay.test.js] testing Arrhenius kinetic decay calculations, remaining days estimations, and high-heat spoilage alerts (2/2 tests passing).

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🛠️ Type of Change

• ⛓️ Smart Contract (Solidity changes, Gas optimization)
• 💻 Frontend (UI/UX, React components)
• ⚙️ Backend / AI ML (Express API, Arrhenius kinetics, Spoilage calculation)
• 📄 Documentation (README, Roadmap updates)
• 🧪 Testing (Jest unit tests)

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🔗 Related Issue

Closes #1289

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🧪 Testing & Verification

• Smart Contracts: npx hardhat test passed? (N/A)
• Backend: npx jest tests/spoilageDecay.test.js passed? (Yes) — 2/2 tests passing in 35s.

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✅ PR Checklist

• My code follows the project's style guidelines.
• I have commented my code, particularly in complex areas (e.g., Arrhenius activation energy constants & humidity multipliers).
• I have updated the documentation accordingly.
• My changes generate no new warnings.

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💬 Additional Notes

• Updated [backend/services/spoilageDetectionService.js]
• Updated [backend/routes/aiRoutes.js]
• Created [backend/tests/spoilageDecay.test.js]

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