Asset previews now show shareable URLs, steadier dialogs, and assorted improvements

Asset previews now have shareable URLs and proper browser history support, and dialogs stay put as their content grows.

Opening an asset preview now shows the canonical /<org>/<library>/assets/<assetId> URL, so you can copy a link to any asset and share it, or reload the page to land on the standalone asset page. Back and Forward move between the previews you opened rather than stepping through every one, and closing a preview always returns you to the grid.

Dialogs are now pinned near the top of the viewport instead of vertically centered. Previously, any dialog whose content changed height would jump around the screen: expanding the context list in a delete confirmation, moving through upload states, or opening the folder tree when linking to a folder. Now the top edge stays fixed and the dialog grows downward, so expansion reads as growth. A fully grown dialog stops the same distance from the bottom of the viewport as its top edge.

• Clicking an asset card in the grid now shows the subtle click style rather than the brighter keyboard focus ring, which is reserved for arrow key navigation and tabbing in.
• Bulk selection state now updates immediately instead of waiting for an unrelated re-render to pick up the change.