Add structured logging with correlation IDs and centralized aggregation

[Smartdevs17]

Description

Logs are unstructured making debugging across services difficult. Implement structured logging with correlation IDs.

Acceptance Criteria

• Structured JSON logging format
• Correlation ID propagation across async boundaries
• Log level configuration per module
• PII redation in logs
• Centralized log aggregation (ELK or Loki)
• Log query dashboard with filtering

Technical Scope

• backend/services/logging.ts
• src/services/
• Edge: async context propagation, log volume management, sensitive field detection