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.

app/dashboard/chats/[id]/loading.tsx

@@ -2,6 +2,7 @@ import Layout from "@/components/layout/layout";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { Skeleton } from "@/components/ui/skeleton";
 import { Loader2 } from "lucide-react";
+import { SnowLoader } from "@/components/snow-loader";
 
 export default function ChatDetailLoading() {
   return (
@@ -18,6 +19,7 @@ export default function ChatDetailLoading() {
 
         {/* Chat window */}
         <div className="border rounded-lg h-[calc(100vh-12rem)] flex flex-col relative">
+          <SnowLoader className="z-0" count={20} />
           {/* Chat messages area */}
           <div className="flex-1 p-4 overflow-hidden">
             <div className="absolute inset-0 flex items-center justify-center z-10 pointer-events-none">