refactor: dockerfile to install all dependencies and prune dev

[josephgoksu]

📋 Description

• adjust backend Dockerfile to install dev deps for the TypeScript build, then prune them for a slimmer final image

🔄 Type of Change

• 🔧 Build/CI changes

🧪 Testing

• I have tested this change locally (docker image now builds once rebuilt via docker-compose up --build)

📱 Screenshots (if applicable)

N/A

🔍 Code Review Checklist

• Code follows the project's coding standards
• Self-review of the code has been performed
• Changes generate no new warnings

📚 Related Issues

N/A

🚀 Deployment Notes

Rebuild the backend container to pick up the Dockerfile changes.

[nullure]

LGTM