feat: improve book reviews, restore detailed privacy policy, fix header logo, add theme toggle, integrate boneyard-js

- Book reviews: add line-clamp for longer review text with expand/collapse per review
- Privacy policy: restore full detailed DSGVO-compliant fallback content
- Header (legal pages): change logo from 'dk' to 'dk0' in circle
- Header (main page): add ThemeToggle for dark/light mode switching
- Skeleton loading: integrate boneyard-js for ReadBooks, CurrentlyReading, Projects
- Add boneyard.config.json and bones/registry.ts placeholder

app/components/Header.tsx

@@ -31,7 +31,7 @@ const Header = () => {
             href={`/${locale}`}
             className="w-10 h-10 flex items-center justify-center rounded-full bg-stone-900 dark:bg-stone-50 text-white dark:text-stone-900 transition-transform hover:scale-105 active:scale-95 shadow-lg"
           >
-            <span className="font-black text-xs tracking-tighter">dk</span>
+            <span className="font-black text-xs tracking-tighter">dk0</span>
           </Link>
 
           {/* Desktop Menu */}