Sheet sets: fly-out submenus, block previews, window-aspect named views

- Row menus open Set category / Place Callout Block as fly-out submenus
  (hover or right press; leftwards when the palette is docked right).
- List of Blocks and Select Block show the Blocks palette's preview.
- VIEW SAVE keeps the window's width/height ratio.
- Placing view content in model space is refused with the reference message.
- Drawings read for views, placement and blocks are cached by modification time.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/view/mod.rs

@@ -3041,7 +3041,7 @@ impl OpenCADStudio {
                 auto_collapse,
             ),
             crate::ui::dock::PanelId::SheetSetManager => {
-                crate::ui::window::sheet_set::view(&self.sheet_set, width, auto_collapse)
+                crate::ui::window::sheet_set::view(&self.sheet_set, width, auto_collapse, side == crate::app::config::DockSide::Right)
             }
         };
         let divider = dock_divider(id);