JSON Trailing Comma Fix Guide

Resolve one of the most common invalid JSON issues before it breaks downstream consumers.

1. Validate with a strict JSON parser, not JavaScript object literals.

2. Remove trailing commas from the last property in objects.

3. Remove trailing commas from the last item in arrays.

4. Reformat payload after edits to spot hidden punctuation issues.

5. Add CI validation for JSON config and API fixtures.

6. Keep one valid and one invalid sample for regression tests.