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/LeaderboardPage.vue

@@ -39,7 +39,7 @@ const record = (b: Bot) => `${b.wins}W - ${b.losses}L`
 </script>
 
 <template>
-  <div class="h-[calc(100vh-4rem)] flex flex-col px-6 py-6 overflow-hidden">
+  <div class="h-[calc(100dvh-4rem)] flex flex-col px-6 py-6 overflow-hidden">
     <div class="max-w-4xl mx-auto w-full flex flex-col flex-1 min-h-0">
 
       <!-- Header -->