feat(static): retain unique badge referrers

[nick-csu]

Summary

• run a Worker only for the Built with Cortex SVG
• retain normalized referrer hostnames in a D1 table with a case-insensitive primary key
• provision and migrate the production database idempotently during deployment
• verify production by submitting the same referrer twice and requiring one row

Validation

• npm run --workspace=@cortex-docs/demo-api build
• npm run --workspace=@cortex-docs/demo-api test
• npx wrangler deploy --dry-run --config packages/demo-api/wrangler.static.jsonc
• local D1 migration and duplicate insert check
• npm run format:check
• npm run lint