feat: comprehensive UI/a11y/i18n fixes and pre-push quality test

- Fix ClientWrappers missing 'about' namespace (MISSING_MESSAGE error)
- Add system/light/dark theme toggle with prefers-color-scheme detection
- Rewrite 404 page with i18n, accessibility, and proper navigation
- Rewrite books page with Header/Footer, i18n, and semantic HTML
- Add i18n keys to About, Footer, and both locale files
- Fix dark mode contrast: text-stone-300/600 -> text-stone-400
- Replace raw hex bg-[#fdfcf8] with bg-stone-50 across all components
- Guard console.error in ChatWidget and manage/page behind NODE_ENV
- Add aria-label to admin login form
- Remove emoji from manage page password toggle
- Update stale dates in privacy-policy and legal-notice
- Fix ScrollFadeIn index->delay prop type error in books page
- Fix privacy-policy and legal-notice landmark structure
- Add pre-push-check.test.ts: 13-category static analysis
  (i18n parity, namespace coverage, key resolution, accessibility,
   email validation, hex colors, emojis, console guards, env docs, types)
- Add explicit i18n check step to CI workflow

app/privacy-policy/page.tsx

@@ -29,7 +29,8 @@ export default function PrivacyPolicy() {
   }, [locale]);
 
   return (
-    <div className="min-h-screen bg-[#fdfcf8] dark:bg-stone-950 transition-colors duration-500">
+    <>
+    <div className="min-h-screen bg-stone-50 dark:bg-stone-950 transition-colors duration-500">
       <Header />
       <main className="max-w-7xl mx-auto px-6 pt-40 pb-20">
 
@@ -150,7 +151,7 @@ export default function PrivacyPolicy() {
                   <p className="text-xl font-light leading-relaxed text-stone-600 dark:text-stone-400">
                     Diese Datenschutzerklärung wird regelmäßig aktualisiert, um den gesetzlichen Anforderungen zu entsprechen. Die jeweils aktuelle Version finden Sie auf dieser Seite.
                   </p>
-                  <p className="text-sm text-stone-400 dark:text-stone-500 mt-6">Letzte Aktualisierung: April 2025</p>
+                  <p className="text-sm text-stone-500 dark:text-stone-400 mt-6">Letzte Aktualisierung: Mai 2025</p>
                 </section>
               </div>
             )}
@@ -196,7 +197,7 @@ export default function PrivacyPolicy() {
               <p className="text-stone-900 dark:text-stone-50 font-bold mb-4">Your connection is private and secure.</p>
               <button
                 onClick={() => {
-                  localStorage.removeItem('cookie-consent');
+                  document.cookie = 'dk0_consent_v1=; path=/; expires=Thu, 01 Jan 1970 00:00:00 GMT'; localStorage.removeItem('cookie-consent');
                   window.location.reload();
                 }}
                 className="text-[10px] font-black uppercase tracking-widest border-b border-stone-300 dark:border-stone-700 pb-1 hover:text-liquid-mint transition-colors"
@@ -208,7 +209,8 @@ export default function PrivacyPolicy() {
           </div>
         </div>
       </main>
+      </div>
       <Footer />
-    </div>
+    </>
   );
 }