UI.10 View overlays: view cube and compass, navigation bar, viewport label, axes icon, in the corners of the drawing

The drafting reference shows four things over the drawing itself: a view cube with a compass (N/E/S/W, "TOP", a WCS drop-down) top right, a navigation bar (a Discord member, zoom, zoom window, orbit) at the right edge, a viewport label "[-][Top][2D Wireframe]" top left, and an axes (UCS) icon bottom left. The engine has no corner places: view-top and view-bottom are full-width strips, and each app draws its own view cube (BimCraft's display modes beside the view cube, GH.3-B) or none. Change: four view-corner places (view-tl, view-tr, view-bl, view-br) in the format, each a small stack of overlays that never take pointer events outside their boxes; shared overlay blocks: viewcube (the app's 3D view orientation through the adapter's views API, with the compass and the named views), navbar (a Discord member, zoom extents, zoom window, orbit, walk from the registry), viewlabel (view name, display mode, scale, the [-] menu with the app's view commands), axes (the app's UCS/axes drawing, or the shared one). Each is a block a layout turns on, so Drafting (UI.12) and Sketch have them and Toolbox does not. Apps keep their own where they have more (BimCraft's display modes feed viewlabel). Test: each overlay present and placed in every app that has 3D, with the drawing's pointer events untouched between them.