fix: iOS PWA bottom nav shifting up in standalone mode

In iOS WebKit standalone (home screen) mode, position:fixed elements
move with the page when the body itself becomes scrollable - unlike
regular Safari where fixed elements stay pinned. The root cause was
body having min-height: 100dvh without overflow: hidden, which allowed
body scroll to occur when content overflowed.

Fix: html and body are now overflow: hidden with fixed height (100% / 100dvh)
so all scrolling is confined to .app-content. Service worker bumped to
shell-v30 to force re-download of reset.css on installed PWAs.

public/styles/reset.css

@@ -21,11 +21,14 @@ html {
   scroll-behavior: smooth;
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
+  /* iOS PWA: verhindert Body-Scroll, der position:fixed-Elemente verschiebt */
+  height: 100%;
+  overflow: hidden;
 }
 
 body {
-  min-height: 100dvh;
-  overflow-x: hidden;
+  height: 100dvh;
+  overflow: hidden;
 }
 
 img, svg, video {