Replace blank home page with a landing page explaining collaborative
route planning. Hero section with "Start Planning" CTA, 5 feature cards
(collaboration, routing, elevation, GPX, no account), secondary CTA
linking to Journal, and footer with privacy/source/attribution links.
All strings in en + de via i18n.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>