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

messages/de.json

@@ -73,6 +73,8 @@
         "finishedAt": "Beendet am",
         "showMore": "{count} weitere anzeigen",
         "showLess": "Weniger anzeigen",
+        "readMore": "Weiterlesen",
+        "collapseReview": "Weniger anzeigen",
         "empty": "In Hardcover fertig gelesene Bücher erscheinen hier automatisch."
       },
       "activity": {