Use window.innerHeight for mobile viewport height on Chrome Android

Set --app-height CSS custom property from window.innerHeight via JS,
which is the only reliable way to get the actual visible viewport on
Chrome Android. Falls back to 100vh if JS hasn't loaded.

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

client/app.js

@@ -90,10 +90,20 @@ class GolfGame {
     }
 
     initMobileDetection() {
+        // Set --app-height custom property to actual visible viewport height.
+        // This works around Chrome Android's 100vh bug where vh includes the
+        // space behind the dynamic URL bar.
+        const setAppHeight = () => {
+            document.documentElement.style.setProperty('--app-height', `${window.innerHeight}px`);
+        };
+        window.addEventListener('resize', setAppHeight);
+        setAppHeight();
+
         const mql = window.matchMedia('(max-width: 500px) and (orientation: portrait)');
         const update = (e) => {
             this.isMobile = e.matches;
             document.body.classList.toggle('mobile-portrait', e.matches);
+            setAppHeight();
             // Close any open drawers on layout change
             if (!e.matches) {
                 this.closeDrawers();