Set up project configuration and base UI components

Initializes the project with necessary configurations, including Replit settings and a .gitignore file. It also introduces foundational UI components for the application, such as buttons, dialogs, and layout elements, likely for the Pomodoro timer application.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 59a5ae27-3c71-459b-b42f-fe14121bf9c3
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/3007b6f6-d03b-45e1-9ed1-7ce8de18ea24/59a5ae27-3c71-459b-b42f-fe14121bf9c3/Uupe4F4

client/src/pages/not-found.tsx

@@ -0,0 +1,21 @@
+import { Card, CardContent } from "@/components/ui/card";
+import { AlertCircle } from "lucide-react";
+
+export default function NotFound() {
+  return (
+    <div className="min-h-screen w-full flex items-center justify-center bg-gray-50">
+      <Card className="w-full max-w-md mx-4">
+        <CardContent className="pt-6">
+          <div className="flex mb-4 gap-2">
+            <AlertCircle className="h-8 w-8 text-red-500" />
+            <h1 className="text-2xl font-bold text-gray-900">404 Page Not Found</h1>
+          </div>
+
+          <p className="mt-4 text-sm text-gray-600">
+            Did you forget to add the page to the router?
+          </p>
+        </CardContent>
+      </Card>
+    </div>
+  );
+}