Add Pino logger for better structured logging

[Nathydre]

• Files to modify : backend/src/utils/logger.ts , replace winston with pino
• Acceptance Criteria :
  • Replace existing logger with Pino
  • Ensure all log statements use structured format
  • Add log levels (debug, info, warn, error)

[oyehimar-bot]

I’m confident I can take on this project because I understand the problem and have the right skills and security. I know how to write secure, well-tested, and clear code, which is exactly what this task needs. The plan is straightforward, and the timeframe is doable for me.

[Richardkingz2019]

Hi maintainer, I would love to work on this issue. I have studied the details of the issue description and I understood the requirements. I shall deliver with qualitative feedback and promptly.