Resolve API Error Responses

Start the "Resolve API Error Responses" loop.

Goal: Standardize API error responses
Max iterations: 10
Between iterations run: npm run test:api-errors
Exit when: Error validation tests pass


Analyze the current API error handling in this codebase. Create a standardized error response format following RFC 7807 Problem Details specification. Apply this format consistently across all API endpoints and error scenarios. Run 'npm run test:api-errors' to validate your implementation. Continue iterating until all error validation tests pass.

Self-pace this loop. After each iteration, run `npm run test:api-errors` and evaluate the output, and only continue if the exit condition is not met (Error validation tests pass). Stop when the exit condition passes or 10 iterations are reached. Give a short status update each pass.