Discourse doesn't ensure guardian check when creating QueryGroupBookmark

Discourse is an open source discussion platform. Prior to versions 2025.12.2, 2026.1.1, and 2026.2.0, missing validate_before_create authorization in Data Explorer's QueryGroupBookmarkable allows any logged-in user to create bookmarks for query groups they don't have access to, enabling metadata disclosure via bookmark reminder notifications. Versions 2025.12.2, 2026.1.1, and 2026.2.0 fix this issue and also make sure validate_before_create throws NotImplementedError in BaseBookmarkable if not implemented, to prevent similar issues in the future. No known workarounds are available.