feat(pricing): add competitor price comparison calculator

- Interactive slider for 50–10,000 members
- Real prices from SEWOBE, easyVerein, ClubDesk, WISO MeinVerein
- Bar chart comparing monthly/yearly costs
- Savings callout showing annual savings vs most expensive competitor
- Feature comparison table (Verband, Website, Kurse, SEPA, Support, etc.)
- SEWOBE Verband warning for 1000+ members
- Uses shadcn/ui components (Card, Badge, Button, Table)
- CTA linking to sign-up
- 4 tiers: Starter (29€), Pro (59€), Verband (199€), Enterprise (349€)

apps/web/app/[locale]/(marketing)/pricing/page.tsx

@@ -6,6 +6,8 @@ import { SitePageHeader } from '~/(marketing)/_components/site-page-header';
 import billingConfig from '~/config/billing.config';
 import pathsConfig from '~/config/paths.config';
 
+import { PricingCalculator } from './_components/pricing-calculator';
+
 export const generateMetadata = async () => {
   const t = await getTranslations('marketing');
 
@@ -23,12 +25,18 @@ async function PricingPage() {
   const t = await getTranslations('marketing');
 
   return (
-    <div className={'flex flex-col space-y-8'}>
+    <div className={'flex flex-col space-y-16'}>
       <SitePageHeader title={t('pricing')} subtitle={t('pricingSubtitle')} />
 
-      <div className={'container mx-auto pb-8 xl:pb-16'}>
+      {/* Pricing tiers */}
+      <div className={'container mx-auto'}>
         <PricingTable paths={paths} config={billingConfig} />
       </div>
+
+      {/* Price comparison calculator */}
+      <div className={'container mx-auto pb-8 xl:pb-16'}>
+        <PricingCalculator />
+      </div>
     </div>
   );
 }