Align impressum page layout with article pages

Update the impressum page to use a max-width of `max-w-4xl` and adjust `PageSideAds` to `contentHalfWidth={448}` to match article page styling.

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client/src/pages/impressum.tsx

@@ -9,8 +9,8 @@ export default function ImpressumPage() {
   return (
     <div className="min-h-screen bg-background">
       <Header />
-      <PageSideAds contentHalfWidth={384} />
-      <main className="max-w-3xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
+      <PageSideAds contentHalfWidth={448} />
+      <main className="max-w-4xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
         <div className="flex items-center gap-3 mb-8">
           <Scale className="w-7 h-7 text-primary" />
           <h1 className="text-3xl font-bold text-foreground" data-testid="text-impressum-title">