Handle empty API responses gracefully

[hadessunxy-code]

/claim #35

Summary

• Add a reusable parseApiResponse helper that returns friendly error objects for missing responses, empty bodies, 204/205 responses, non-OK responses, and malformed JSON.
• Add focused regression coverage for valid JSON, null responses, empty responses, 204 responses, and bad JSON.
• Include the new API response test in npm test.

Validation

• npm test