Disable Christmas theme and improve layout skeleton

Christmas decorations and theme logic have been disabled throughout the app, including the isDecember utility, layout, and related imports. Layout now shows a skeleton UI while mounting to prevent layout shift. Minor improvements to RevenueChart tooltip colors and ChatDetail request headers for better consistency.

components/analytics/RevenueChart.tsx

@@ -94,9 +94,9 @@ export default function RevenueChart({ timeRange, hideNumbers = false }: Revenue
     if (active && payload && payload.length) {
       const data = payload[0].payload;
       return (
-        <div className="bg-white p-3 border border-gray-200 rounded-lg shadow-lg">
-          <p className="text-sm font-medium text-gray-900">{data.formattedDate}</p>
-          <p className="text-sm text-blue-600">
+        <div className="bg-background p-3 border border-border rounded-lg shadow-lg">
+          <p className="text-sm font-medium text-foreground">{data.formattedDate}</p>
+          <p className="text-sm text-blue-600 dark:text-blue-400">
             Revenue: <span className="font-semibold">{hideNumbers ? '£***' : formatGBP(data.revenue)}</span>
           </p>
           <p className="text-sm text-green-600">

components/dashboard/ChatDetail.tsx

@@ -473,7 +473,7 @@ export default function ChatDetail({ chatId }: { chatId: string }) {
             content: newMessage 
           }),
           headers: {
-            'Content-Type': 'application/json'
+            'Content-Type': 'application/json; charset=utf-8'
           }
         });
       }

components/layout/layout.tsx

@@ -23,20 +23,39 @@ export default function Layout({ children }: LayoutProps) {
 
   useEffect(() => setMounted(true), [])
 
-  if (!mounted) return null
+  // Show skeleton while mounting to prevent layout shift
+  if (!mounted) {
+    return (
+      <div className="flex h-screen">
+        <Sidebar />
+        <div className="w-full flex flex-1 flex-col">
+          {!isChatDetailPage && !isAdminPage && (
+            <header className="h-16 border-b border-border flex items-center justify-end px-6 bg-background">
+              <div className="flex items-center space-x-2">
+                <div className="h-10 w-10 bg-muted animate-pulse rounded" />
+              </div>
+            </header>
+          )}
+          <main className={`flex-1 ${isChatDetailPage ? 'p-0 overflow-hidden' : 'p-6 overflow-auto'} bg-background relative`}>
+            {children}
+          </main>
+        </div>
+      </div>
+    )
+  }
 
   return (
-    <div className={`flex h-screen ${theme === "dark" ? "dark" : ""}`}>
+    <div className="flex h-screen">
       <Sidebar />
       <div className="w-full flex flex-1 flex-col">
         {!isChatDetailPage && !isAdminPage && (
-          <header className="h-16 border-b border-border flex items-center justify-end px-6">
+          <header className="h-16 border-b border-border flex items-center justify-end px-6 bg-background">
             <div className="flex items-center space-x-2">
               <UnifiedNotifications />
             </div>
           </header>
         )}
-        <main className={`flex-1 ${isChatDetailPage ? 'p-0 overflow-hidden' : 'p-6 overflow-auto'} dark:bg-[#0F0F12] relative`}>
+        <main className={`flex-1 ${isChatDetailPage ? 'p-0 overflow-hidden' : 'p-6 overflow-auto'} bg-background relative`}>
           {children}
         </main>
       </div>