Replaced all inline error messages with the standardized `api_error` helper for consistent error response formatting. This improves clarity, maintainability, and ensures uniform error structures across the application. Updated logging for collector failures to include error class and switched to warning level for target unreachable scenarios.
Introduced standardized error response formats for API errors, including middleware for consistent request IDs and exception handlers. Updated the frontend to parse and process these error responses, and documented the error format in the README for reference.
