feat: landing page — minimal dark one-pager with Dockerfile

Single static HTML page for RückenfrAI ("KI, die dir den Rücken
freihält"). Dark theme, inline CSS, Inter font. Sections: hero with
terminal mockup, features (email/voice/calendar/tasks), how it works,
waitlist CTA (mailto). nginx Dockerfile + docker-compose for Dokploy.

Dockerfile

@@ -0,0 +1,3 @@
+FROM nginx:alpine
+COPY index.html /usr/share/nginx/html/index.html
+EXPOSE 80