Stellar Light and ATLAS exporters #28

Why

Two ecosystem directories want this data in their own shape.

In this repo today

export/build.py builds the public dataset and export/render.py writes JSON and YAML plus its schema to apps/web/public/.

What to build

• export/stellarlight.py: maps projects to rows matching Stellar Light's hackathon submissions index (id, event, name, tagline, repo, repo verified, verification evidence, builders, official status).
• export/atlas.py: maps repos to ATLAS rows (repo, project, program, person or org, language, chain evidence).
• A --target option on export for each, writing stellarlight.json and atlas.json next to the main dataset, and a --diff flag that prints what changed since the last export.
• Publish a JSON schema for each next to the existing schema files in apps/web/public/schema/.

Acceptance criteria

• A test validates every exported row against its schema.

See CONTRIBUTING.md for conventions.