JSON schema export from pydantic models #32

Why

Anyone building on the data should be able to find and validate against its schemas.

In this repo today

uv run hackproof export already writes the dataset and a versioned schema (apps/web/public/schema/hackathon-export-1.x.json and .yml), and tests/test_export.py validates the export against it. API responses (schemas.py) have no published schema.

What to build

• Write *.schema.json for the public API models in schemas.py into apps/web/public/schema/ with $id URLs and a version, through a subcommand or as part of export.
• An index.json listing every published schema and version.
• A "Data" section in the README linking to the index.

Acceptance criteria

• A test validates a sample response of each API model against its schema.
• The index lists the existing export schema versions.

See CONTRIBUTING.md for conventions.