Add Christmas theme and snow effects for December

Introduces a Christmas theme that activates in December, including themed colors, subtle background patterns, and snowflake effects on loading screens. Adds a reusable SnowLoader component and utility for December detection. Updates layout and loading components to conditionally apply decorations and styles only during December.

components/dashboard/page-loading.tsx

@@ -3,6 +3,7 @@
 import { Skeleton } from "@/components/ui/skeleton";
 import { Card } from "@/components/ui/card";
 import { Loader2 } from "lucide-react";
+import { SnowLoader } from "@/components/snow-loader";
 
 interface PageLoadingProps {
   title?: string;
@@ -30,6 +31,7 @@ export default function PageLoading({
 
       {/* Main content skeleton */}
       <Card className="relative overflow-hidden">
+        <SnowLoader className="z-0" count={25} />
         <div className="absolute inset-0 flex items-center justify-center z-10 pointer-events-none">
           <div className="flex flex-col items-center justify-center bg-background/80 backdrop-blur-[2px] p-6 rounded-lg shadow-sm">
             <Loader2 className="h-10 w-10 animate-spin text-primary mb-3" />