fix: bottom-nav-inner must be column not row — tabs stacked above buttons

flex-direction:row put the tab strip and icon buttons side-by-side,
both fighting for 100% width, making them overflow and appear huge.
Column stacks the Bibliothek/Entdecken tabs on top, icon row below.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v21';
+const CACHE = 'ns-v22';
 const PRECACHE = ['/', 'index.html', 'styles.css', 'app.js', 'sw.js', 'manifest.json', 'icon.svg'];
 const SKIP_URLS = ['/rest/stream', '/rest/download', '/config.js'];