IAV-260/feat(core): add unified exception handling components

Summary

Introduces a unified exception handling in iavia-common to standardize error responses across all microservices.

Changes

• ApiErrorResponse: Standardized error response format with origin, code, details, and timestamp fields
• ServiceOrigin: Enum listing all microservices for traceability
• UpstreamServiceException: Exception class for propagating errors from upstream services
• UpstreamErrorHandler: Utility handling both compliant and non-compliant upstream responses
• ExternalServiceLogHelper: Logging helper for consistent error tracking

Benefits

• Frontend i18n support via error codes
• Consistent error format across all services
• Secure: no stack traces or sensitive data exposed to clients
• Improved traceability in distributed architecture

Related Documentation

See the iavia unified exception handling guide (PDF) for implementation details.

Closes IAV-260