Add new pages and improve blog content display functionality

Implement new routes for articles, categories, and individual articles. Update the UI to display articles with improved content rendering, including safe HTML and media embeds. Refactor storage to use a database and add image upload capabilities.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 413891e8-d784-4bea-b9f5-91a5a68316b4
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Replit-Commit-Event-Id: b96b221e-0ed6-418f-80df-e4670bf5ba4b
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client/src/pages/not-found.tsx

@@ -1,21 +1,21 @@
-import { Card, CardContent } from "@/components/ui/card";
-import { AlertCircle } from "lucide-react";
+import { Link } from "wouter";
+import { Button } from "@/components/ui/button";
+import Header from "@/components/header";
 
 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 className="min-h-screen bg-background">
+      <Header />
+      <div className="flex flex-col items-center justify-center py-32 px-4">
+        <h1 className="text-6xl font-bold text-primary mb-4" data-testid="text-404">404</h1>
+        <p className="text-xl text-foreground mb-2">Seite nicht gefunden</p>
+        <p className="text-muted-foreground mb-8 text-center max-w-md">
+          Die gesuchte Seite existiert nicht oder wurde verschoben.
+        </p>
+        <Link href="/">
+          <Button data-testid="button-back-home">Zur Startseite</Button>
+        </Link>
+      </div>
     </div>
   );
 }