feat(ui): redesign landing page and update styling

Overhaul landing page design with updated CSS, Tailwind config, and
i18n translations across all supported languages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/i18n/de.json

@@ -224,7 +224,13 @@
     "documentation": "Dokumentation",
     "api_reference": "API-Referenz",
     "support": "Support",
-    "copyright": "2026 CERTifAI. Alle Rechte vorbehalten."
+    "copyright": "2026 CERTifAI. Alle Rechte vorbehalten.",
+    "pill_gdpr": "DSGVO-Nativ",
+    "pill_self_hosted": "Selbst gehostet",
+    "pill_eu": "EU-Souveraen",
+    "preview_models": "Aktive Modelle",
+    "preview_tokens": "Tokens / Monat",
+    "preview_spend": "Gesamtausgaben"
   },
   "article": {
     "read_original": "Originalartikel lesen",