Photo lightbox stays centered at any scale

Fixed lightbox expanding off-screen with large photo counts; main image now stays centered and filmstrip scrolls.

Bug Fixes

The photo lightbox modal was expanding thousands of pixels wide when viewing projects with many photos (100+), pushing the main image off-screen and hiding the navigation buttons.

This happened because the container was sizing itself to fit its widest child — the thumbnail filmstrip — instead of staying within the dialog bounds. Now the lightbox respects its container width, the main image stays centered and visible, and the thumbnail filmstrip scrolls horizontally when needed.

Affects both the in-app photo viewer and the share-portal preview.