feat: AI/KI disclosure footer — shared/ai-disclosure.js + all 54 sites

Self-injecting script following impressum.js pattern:
- data-tone attribute: playful | serious | minimal | none
- Reads document.documentElement.lang for KI (de) vs AI (en)
- MutationObserver on lang attr for i18n toggle compat
- All tones link to msbls.de/ki
- Injected into all 54 custom sites with data-tone="playful"
- Template infra: base.html includes script, render.sh reads disclosure.tone
- disclosure.tone added to 3 example site.yaml files

Implements m/onepager#2

sites/julietensity.de/index.html

@@ -589,6 +589,7 @@
     </div>
   </footer>
 
+  <script src="/shared/ai-disclosure.js" data-tone="playful"></script>
   <script src="/shared/i18n.js"></script>
 </body>
 </html>