Create a proper public landing page

[enaboapps]

Summary\nReplace the current / redirect with a real public homepage for Podium.\n\n## Scope\n- Make / publicly accessible\n- Redirect signed-in users from / to /library\n- Add a proper landing page for signed-out users\n- Keep the rest of the app protected\n- Highlight import, delivery preparation, voice selection, and offline readiness\n- Keep the first pass focused on hero, how-it-works, features, and CTA sections\n\n## Acceptance Criteria\n- Signed-out users can open / without being sent to Clerk immediately\n- Signed-in users visiting / land on /library\n- Signed-out users still cannot access /library\n- Public homepage does not show the offline boot splash before content renders\n- CTAs navigate correctly to /sign-up and /sign-in\n-

pm run build passes\n