fix: mobile — scale sprites to canvas size, fix viewport scroll

- Add scale factor (SF) based on canvas height so bots and referee
  shrink proportionally on small screens (reference: 500px)
- Scale judge chair/ladder dimensions with SF
- Push judge seat lower on small canvases so it stays visible
- Use 100dvh instead of 100vh to account for mobile browser chrome
  (address bar, tab bar) — eliminates scroll under browser UI
- App root uses dvh, main area uses min-h-0 + overflow-y-auto

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

frontend/src/pages/FightPage.vue

@@ -649,7 +649,7 @@ function stopAutoBattle() {
 </script>
 
 <template>
-  <div class="h-[calc(100vh-4rem)] flex flex-col px-2 sm:px-3 py-2 sm:py-3 overflow-hidden">
+  <div class="h-[calc(100dvh-4rem)] flex flex-col px-2 sm:px-3 py-2 sm:py-3 overflow-hidden">
     <div v-if="isLoading" class="flex-1 flex items-center justify-center">
       <p class="font-display text-text-muted animate-pulse tracking-wider">LOADING FIGHT...</p>
     </div>