Implement DDS-005 layout shells

[klaasnicolaas]

Summary

Implements DDS-005 by replacing the starter-kit public and authenticated shell placeholders with a DDS-oriented public layout and management dashboard baseline.

Changes

• Adds a dedicated public layout with DDS header, mobile navigation, and footer.
• Reworks the public home page from starter content into a DDS shell baseline.
• Replaces the dashboard placeholder with a DDS management entrypoint.
• Updates app logo treatment, management sidebar/header navigation, and sidebar footer links.
• Adds a DDEV/Vite CORS allowance so dev-server assets load from the DDEV app origin.
• Updates the backlog with project showcase follow-up tickets.
• Tightens the home feature test to assert the Inertia page component.

Validation

• vendor/bin/pint --dirty --format agent
• php artisan test --compact tests/Feature/ExampleTest.php tests/Feature/DashboardTest.php
• npm run types:check
• npm run lint:check
• npm run build
• npx prettier --check docs/backlog/initial-build-backlog.md

This PR is intentionally a layout shell baseline, not final visual polish or final project/event content modeling.