Menu pinned bar and layout

This update makes menus behave predictably on phone and desktop, gives the
Share Folder dialog one consistent layout, and finally shows your real page in
social previews.

Menus That Stay Put
Submenus like View style and Sort by now wait a moment before opening, the same
way the main menu does — passing your pointer over a row no longer flings a
flyout open. On phones, a submenu opens right where you tapped instead of
appearing far down the screen, and the row you tapped no longer disappears
behind it.

Controls You Can Always See
Menu buttons keep their translucent glass finish for as long as their menu is
open, so a trigger no longer fades away the moment you move onto the panel.
Wallpaper cards use the same finish, with white icons that stay legible on any
photo. In the sidebar, hovering a folder no longer draws bars at its edges, and
the folder you're in is marked by its background alone.

Pinned Bar, Tidied Up
Unpin appears once, at the top of the menu where you'd look for it, instead of a
second time inside More.

Share Folder, One Layout
Link, Customize, Publish, Team and Analytics now share a single column width
that lines up with the thumbnail card, so nothing sprawls wider than its
neighbour. Analytics cards arrange themselves by the space they have, and in
Customize the background card no longer covers the Blur, Dim and Text & Icon
controls.

Social Previews That Look Like Your Page
Share a folder and the preview image is your page: round icons on a white
canvas, labels centred beneath them. Titles that don't fit end in an ellipsis
instead of being cut mid-letter, icons that can't be decoded fall back to a
lettered chip, and the old icon-and-title header is gone.

Fixes and Improvements
- Social previews were empty for every shared page; they now read from the
bookmark database directly.