Use packaged native core and remote demo dataset

[adsharma]

Summary

• Use the packaged @ladybugdb/core native binding in development and production.
• Remove the Ladybug submodule dependency and stale native build script.
• Fetch the tutorial demo dataset from ladybugdb/demo-db on Hugging Face.
• Resolve relative dataset COPY paths against the selected local dataset directory.
• Document how to regenerate the checked-in ANTLR parser from a temporary Ladybug checkout.

Why

The Explorer runtime no longer needs the full Ladybug source tree to start locally. Native modules are provided by the npm package, and the tutorial dataset now comes from a dedicated Hugging Face dataset instead of sparse-checking out the Ladybug repo.

Validation

• npm run fetch-datasets
• Loaded Tutorial Dataset through /api/datasets/Tutorial%20Dataset/copy and confirmed all node and relationship tables copied successfully.