Looking at the points you made and examples, I would cobble a similar tool with Django, writing only CLI commands with no HTTP endpoints. And most LLMs are already fluent in Django.

- Schemas and relationships live in models.py, actual data is persisted in Sqlite - I can dump to JSON or XML with Django utils for LLMs - Query engine can simplify reuse Django syntax, like `Firm.objects.get(owner_name__like="john", date__gt=2015)`, fetch related names, aggregate subqueries - Format as tables