[Backend] Create structured logging service

[SYLVIANNORUKA]

Description: Implement structured JSON logging across all modules to replace ad hoc console logging.

Requirements:

• Handle request-scoped log context
• Track correlation ID per request
• Validate log level configuration per environment
• Manage sensitive field redaction in logs
• Provide log output in JSON format

Acceptance Criteria:

• Request-scoped context is handled
• Correlation ID is tracked per request
• Log level configuration is validated
• Field redaction works
• JSON log output is provided

Technical Details:

Files: backend/src/modules/../common/logging/logger.module.ts, src/main.ts
Libraries: nestjs-pino, pino-http