Make AI chat fullscreen work

Fix: wire AIChat to Browser fullscreen API, aligning its behavior with game pages. Import and use useBrowserFullscreen, store fullscreen state, ensure Escape exits fullscreen, and toggle via a consistent fullscreen handler (removing non-functional placeholder). This brings true fullscreen for AI chat along with consistent UX with games.

X-Lovable-Edit-ID: edt-2cec4af2-d3d6-49ef-93f8-6cb09b300ed6

src/pages/AIChat.tsx

@@ -8,6 +8,7 @@ import { useSettings } from '@/contexts/SettingsContext';
 import { useAchievements, incrementAiMessageCount } from '@/contexts/AchievementsContext';
 import { useToast } from '@/hooks/use-toast';
 import GlitchText from '@/components/GlitchText';
+import { useBrowserFullscreen } from '@/hooks/useGameDimensions';
 import MessageContent from '@/components/MessageContent';
 import { AI_PROVIDERS, AIProvider, getProvider, CUSTOM_API_STORAGE_KEY } from '@/lib/aiProviders';
 import {
@@ -82,6 +83,7 @@ const AIChat = () => {
   const { playSound } = useSettings();
   const { checkAiAchievements } = useAchievements();
   const { toast } = useToast();
+  const { enterFullscreen, exitFullscreen } = useBrowserFullscreen();
 
   // Persist messages to localStorage
   useEffect(() => {
@@ -109,12 +111,24 @@ const AIChat = () => {
     const handleEscape = (e: KeyboardEvent) => {
       if (e.key === 'Escape' && isFullscreen) {
         setIsFullscreen(false);
+        exitFullscreen();
         playSound('click');
       }
     };
     window.addEventListener('keydown', handleEscape);
     return () => window.removeEventListener('keydown', handleEscape);
-  }, [isFullscreen, playSound]);
+  }, [isFullscreen, playSound, exitFullscreen]);
+
+  const toggleFullscreen = async () => {
+    if (!isFullscreen) {
+      setIsFullscreen(true);
+      await enterFullscreen();
+    } else {
+      setIsFullscreen(false);
+      await exitFullscreen();
+    }
+    playSound('click');
+  };
 
   useEffect(() => {
     if (scrollRef.current) {
@@ -367,10 +381,6 @@ const AIChat = () => {
     }
   };
 
-  const toggleFullscreen = () => {
-    setIsFullscreen(!isFullscreen);
-    playSound('click');
-  };
 
   return (
     <motion.div