feat(editor): fold canvas display controls into one Display dropdown (pascalorg#370)

Replace the seven separate display-control buttons in the canvas toolbar
(render, theme, edges, grid, shadows, units, camera) with a single
"Display" dropdown, matching the simplification already shipped in the
hosted editor. Grid, shadows, camera and units are direct toggles that
keep the menu open; render, edges and theme are submenus.

Portal DropdownMenuSubContent so the side-opening submenus escape the
parent content's overflow-x-hidden clip, and re-export the submenu
primitives (Sub/SubTrigger/SubContent/Separator) from @pascal-app/editor.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Aymericr