🧪 Add test for generic error handler (500)

[shenald-dev]

🎯 What: The generic error handler (catching unexpected 500 errors) was lacking test coverage.
📊 Coverage: A new test case has been added to tests/api.test.js to simulate an internal server error by mocking crypto.randomUUID(). This ensures the API returns a proper 500 Internal server error JSON response and prevents stack traces from leaking to the client.
✨ Result: Increased test coverage and improved reliability by guaranteeing that unexpected server failures are handled gracefully without exposing sensitive internal details.

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PR created automatically by Jules for task 6300726740253245530 started by @shenald-dev

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