Fix iframe recursion and remove all localStorage/cookies site-wide

- Add target="_top" to all ← SPACE / back-to-root links so navigating
  back to index.html breaks out of the content iframe instead of loading
  it recursively inside itself (Images, Music, Watchlists hubs)
- Remove all localStorage usage: visited-star tracking in index.html
  (resets each visit, no persistence without storage), and lightbox
  "show once" guards in all section pages (lightboxes now show on every
  load — Videos, Watchlists, Music). build.py templates updated so
  future generated pages stay clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Music/music-template.html

@@ -535,10 +535,7 @@
         document.addEventListener('DOMContentLoaded', () => {
             // --- Lightbox ---
             const lightbox = document.getElementById('lightbox');
-            if (!localStorage.getItem('music-oldmusicandmvs-seen')) {
-                lightbox.style.display = 'flex';
-                localStorage.setItem('music-oldmusicandmvs-seen', '1');
-            }
+            lightbox.style.display = 'flex';
 
             const closeLightbox = () => { lightbox.style.display = 'none'; };