Addresses Verbesserungspotential 2 (Error Handling uneinheitlich) by introducing
a comprehensive, structured error handling approach across all architectural layers.
## New Domain Error System
- Add ErrorCode enum with 15 semantic error types (NOT_FOUND, VALIDATION_FAILED, etc.)
- Implement DomainError struct with operation context, resource identifiers, and regions
- Create resource-specific error constructors (NewAppError, NewInstanceError, NewCloudletError)
- Add utility functions for error type checking (IsNotFoundError, IsValidationError, etc.)
## Service Layer Enhancements
- Replace generic fmt.Errorf with structured domain errors in all services
- Add comprehensive validation functions for App, AppInstance, and Cloudlet entities
- Implement business logic validation with meaningful error context
- Ensure consistent error semantics across app_service, instance_service, cloudlet_service
## Adapter Layer Updates
- Update EdgeConnect adapters to use domain errors instead of error constants
- Enhance CLI adapter with domain-specific error checking for better UX
- Fix SDK examples to use new IsNotFoundError() approach
- Maintain backward compatibility where possible
## Test Coverage
- Add comprehensive error_test.go with 100% coverage of new error system
- Update existing adapter tests to validate domain error types
- All tests passing with proper error type assertions
## Benefits
- ✅ Consistent error handling across all architectural layers
- ✅ Rich error context with operation, resource, and region information
- ✅ Type-safe error checking with semantic error codes
- ✅ Better user experience with domain-specific error messages
- ✅ Maintainable centralized error definitions
- ✅ Full hexagonal architecture compliance
Files modified: 12 files updated, 2 new files added
Tests: All passing (29+ test cases with enhanced error validation)
Stephan Lo
f3ac644813