added substrate example

[christian-posta]

No description provided.

[christian-posta]

Heads up on the deploy check

The deploy job is failing at the Create website preview step, not at the build. The Wrangler action errors with:

In a non-interactive environment, it's necessary to set a CLOUDFLARE_API_TOKEN environment variable for wrangler to work.

That string only appears when secrets.CLOUDFLARE_API_TOKEN resolves to an empty value in the workflow run. The workflow file itself is correct on this branch (npm ci + wrangler deploy --minify, matching the pre-#385 layout). The next build / npm run build:worker step is passing.

This needs a repo-settings fix that I can't make from a PR:

• Verify CLOUDFLARE_API_TOKEN and CLOUDFLARE_ACCOUNT_ID exist under Settings → Secrets and variables → Actions (not just under an Environment that isn't wired to PR runs).
• If they're scoped to a GitHub Environment, make sure the deploy job opts into that environment via environment: in .github/workflows/preview.yaml, otherwise PR runs won't see the secrets.
• Confirm the token still has Workers deploy permissions on the account CLOUDFLARE_ACCOUNT_ID points to.

Nothing in this PR's diff touches CI auth — happy to rebase if any infra fix lands on main.