Fix guest mode, free tab, 3D models, and settings panel

- Guest mode: heartbeat no longer shows license popup for unauthenticated users
- Free tab: server-side addon_content_access=Free filter applied (was client-side only, showed no results)
- 3D Models: accept GLB format alongside GLTF so assets are no longer hidden
- Settings panel: guests now see Plan:Guest + Activate License button instead of Plan:Active + Logout

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