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/HeaderClient.tsx

@@ -5,6 +5,7 @@ import { SiGithub, SiLinkedin } from "react-icons/si";
 import Link from "next/link";
 import { usePathname, useSearchParams } from "next/navigation";
 import type { NavTranslations } from "@/types/translations";
+import { ThemeToggle } from "./ThemeToggle";
 
 // Inline SVG icons to avoid loading the full lucide-react chunk (~116KB)
 const MenuIcon = ({ size = 24 }: { size?: number }) => (
@@ -128,6 +129,7 @@ export default function HeaderClient({ locale, translations }: HeaderClientProps
                 >
                   DE
                 </Link>
+                <ThemeToggle />
               </div>
             </nav>
 
@@ -188,7 +190,7 @@ export default function HeaderClient({ locale, translations }: HeaderClientProps
           </nav>
 
           {/* Language Switcher Mobile */}
-          <div className="flex gap-2 mt-6 pt-6 border-t border-stone-200">
+          <div className="flex items-center gap-2 mt-6 pt-6 border-t border-stone-200">
             <Link
               href={enHref}
               onClick={() => setIsOpen(false)}
@@ -211,6 +213,7 @@ export default function HeaderClient({ locale, translations }: HeaderClientProps
             >
               DE
             </Link>
+            <ThemeToggle />
           </div>
 
           <div className="mt-8 pt-6 border-t border-stone-200">