ci: add Terraform validation workflow

[AnzalKhan16]

📌 Overview
Added a dedicated GitHub Actions workflow (terraform.yml) to automatically validate our Terraform infrastructure configurations. This workflow runs on pushes or pull requests involving files in the infrastructure/ directory. It ensures our Infrastructure as Code (IaC) uses consistent formatting via terraform fmt -check, initializes successfully using a credential-less backend (terraform init -backend=false), and is syntactically sound via terraform validate. The Terraform CLI version is locked to 1.5.7 to ensure consistency between local development and CI environments.

🛠️ Type of Change
[ ] ⛓️ Smart Contract (Solidity changes, Gas optimization)
[ ] 💻 Frontend (UI/UX, React components, Tailwind)
[ ] ⚙️ Backend (API routes, MongoDB schemas, Middleware)
[ ] 📄 Documentation (README, Roadmap updates)
[x] 🧪 Testing (CI/CD Pipeline, DevOps & Infrastructure as Code)

🔗 Related Issue
Closes #847

🧪 Testing & Verification
Smart Contracts: npx hardhat test passed? (NA)
Frontend: Verified on Mobile/Desktop responsiveness? (NA)
Integration: Verified ethers.js connectivity with local/testnet node? (NA)
Terraform: Workflow successfully triggered on file modification and executes fmt/init/validate without needing AWS credentials? (Yes)

📸 Screenshots / Demos
(N/A - Infrastructure workflow updates only)

✅ PR Checklist
[x] My code follows the project's style guidelines.
[x] I have commented my code, particularly in complex areas.
[x] I have updated the documentation accordingly.
[x] My changes generate no new warnings.

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