Fix iOS PWA black gap with oversized background fallback

The viewport height can be miscalculated on iOS PWA initial load,
causing position:fixed elements to stop short of the physical
screen edge. Two fixes:
- Add min-height: -webkit-fill-available to html/body
- Add body::after with inset: -100px as a background safety net
  that extends beyond the viewport to cover any gap

Author: rgilks

static/style.css

@@ -44,12 +44,13 @@ html,
 body {
   width: 100%;
   height: 100%;
+  min-height: 100vh;
+  min-height: 100dvh;
+  min-height: -webkit-fill-available;
   overscroll-behavior: none;
 }
 
 body {
-  min-height: 100vh;
-  min-height: 100dvh;
   overflow: hidden;
   color: var(--text);
   font-family: var(--font-display);
@@ -71,6 +72,15 @@ body::before {
   opacity: 0.7;
 }
 
+body::after {
+  content: '';
+  position: fixed;
+  inset: -100px;
+  background: var(--bg);
+  z-index: -1;
+  pointer-events: none;
+}
+
 #gameCanvas {
   position: fixed;
   inset: 0;