Extract shared filepond logic into src/FilepondHandler.php class.
Admin filepond endpoints delegate to the handler after AdminAuth check.
New partage filepond endpoints at /partage/actions/filepond/ verify
share_active session flag + CSRF token, no admin auth required.
JS reads filepond-base meta tag to determine endpoint path:
- Admin pages: /admin/actions/filepond (via head.php isAdmin check)
- Partage form: /partage/actions/filepond (explicit meta)
partage/index.php sets share_active = true on form render, cleans up on
successful submit. Partage process endpoint rate-limited to 30/5min per
session. No nginx changes needed — /partage/ location already handles
PHP without auth_basic.
