IAV-691/feat(customer-care): Integrate unified exception handling

Summary

Integrates the unified exception handling from iavia-common into iavia-agent-service-customer-care, ensuring standardized error responses across all service layers.

Changes

Modified

• GlobalExceptionHandler: Refactored to produce ApiErrorResponse with origin, code, details, and timestamp
• BusinessErrorCode: Expanded to 100+ error codes organized by domain (Agent, Language, Instructions, Workflow, etc.)

Added

• BusinessErrorCodeTest: Validation suite ensuring:
  • All codes are unique
  • All codes follow pattern ^[A-Z0-9]{4}-\d{3}$
  • All messages are unique, non-empty, and properly formatted

Integrated

Unified exception handling applied across all layers:

Layer	Classes
External Services	FileManagerServiceImpl, N8nServiceImpl, UserServiceImpl
Helpers	AgentCreationHelper, AgentValidationHelper, UserHelper, WebhookHelper
Business Services	AgentServiceImpl, AgentCustomInstructionServiceImpl, AgentStandardInstructionServiceImpl, AgentSystemPromptConfigServiceImpl, ConfigStandardInstructionServiceImpl, MainAgentWizardServiceImpl, SubAgentServiceImpl

Benefits

• Consistent error format for frontend i18n mapping
• Upstream errors propagated with original source identification
• No sensitive technical details exposed to clients
• Comprehensive test coverage for error code integrity

Dependencies

Requires iavia-common with unified exception handling components (see MR: https://mc-git.com/iavia/iavia-common/-/merge_requests/67)

Related Documentation

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

Closes IAV-261