feat(media): Beheer -> Media — image library with usage + cleanup of orphan files
A new /admin/media page lists uploaded images (storage/media/post-images), shows how many posts use
each, lets you copy a URL, and deletes unused files — including the loop-MP4 + poster siblings of an
animated cover. The Beheer "Audio" nav link becomes "Media" (Audio stays a tab linking to
/admin/audio) so the nav doesn't grow. Mounted unconditionally (works in lite/no-audio mode).
- src/routes/admin-media.js — list / delete / cleanup (path-traversal-safe, god-only)
- src/views/pages/admin-media.ejs — grid + copy/delete/cleanup (CSP-safe nonce'd script)
- server.js mount; admin.ejs nav Audio->Media; i18n nl/en/de
Co-Authored-By: Claude <noreply@…>