docs: Simplify JSON tutorial, add test outputs

- Simplified json-type.ipynb to focus on insert/fetch only
- Removed complex JSON path queries (not portable across backends)
- Added test output logs for MySQL and PostgreSQL runs

Test results:
- MySQL: 21/21 passed
- PostgreSQL: 21/21 passed

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko