Changes

landing: proper Android download badge, reused in the footer

Replaces the flat outline-icon button with a badge in the visual language people
actually recognise: dark pill, mark on the left, small kicker over a bold line,
and the Android robot drawn inline in its own green (#3DDC84).

Deliberately NOT the official "Get it on Google Play" badge. That artwork is
Google's trademark and licensed only for links pointing at a Play Store listing;
this link is a direct APK download, so copying it would be both a trademark
problem and a false claim to the visitor. Same recognition, honest wording
("Direkt-Download / Android APK").

Extracted as AndroidBadge.vue with a `compact` variant so the app section and the
footer cannot drift apart. Until an APK exists the badge renders as a disabled
span (not a dead link) with its own aria-label; set `available` to switch it on.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
 (commit: 88fb8db)