fix: viewport-fixed layout on all pages for mobile

- Replace 100vh with 100dvh everywhere (accounts for mobile browser chrome)
- DocsPage: viewport-fixed with tabs pinned, tab content scrolls internally
- BotProfilePage: overflow-hidden outer, internal scroll container
- JoinBoutPage: viewport-fixed with internal overflow scroll
- HumanFightPage: viewport-fixed, flex-1 content area with internal scroll
- All other pages: vh → dvh for correct mobile sizing

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

frontend/src/pages/HomePage.vue

@@ -315,7 +315,7 @@ onUnmounted(() => {
 </script>
 
 <template>
-  <div class="h-[calc(100vh-4rem)] flex flex-col items-center justify-center px-6 overflow-hidden relative">
+  <div class="h-[calc(100dvh-4rem)] flex flex-col items-center justify-center px-6 overflow-hidden relative">
     <!-- Crowd characters floating around edges -->
     <template v-for="(c, i) in crowd" :key="i">
       <SpritePreview