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/JoinBoutPage.vue

@@ -406,8 +406,8 @@ function handleSignOut() {
 </script>
 
 <template>
-  <div class="min-h-[calc(100vh-4rem)] flex flex-col items-center justify-center px-6 py-8 overflow-y-auto">
-    <div class="max-w-md w-full slide-up">
+  <div class="h-[calc(100dvh-4rem)] flex flex-col items-center justify-center px-6 overflow-hidden">
+    <div class="max-w-md w-full slide-up overflow-y-auto max-h-full py-4">
 
       <!-- STEP: LOGIN -->
       <template v-if="step === 'login'">