[gcomneno]

Summary

Add a fixed, bilingual, read-only consumer showcase to the public Demo homepage.

• Ombre Quotidiane — verified public link.
• Universi Condivisi — text only; public URL pending verification.
• Club dell'Assurdo — verified public link.

The section is visible exclusively in Demo runtime and remains independent of guest authoring readiness.

Architecture

• Preserve Visitor, Local, Hosted and invalid runtime isolation.
• No new authoring capability, mutation endpoint or content model.
• No changes to authentication, CSRF, session budgets or repository authority.
• Keep the showcase separate from catalog creations.

Verification

• npm test: 964 passed, 0 failed (independent terminal execution).
• npm run check: passed.
• npm run content:validate: passed.
• npm run build: passed.
• git diff --check: passed.

Release boundary

Integration into the separate atelier-kit-demo-sandbox repository and deployment to atelier-kit-public-demo are explicitly out of scope for this PR.

Closes #371