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>

locales/ru-RU/opencadstudio.ftl

@@ -4396,6 +4396,8 @@ view =
     .ss-new-sheet-location = New sheet location
     .ss-remove-subset = Remove Subset
     .ss-rename-subset = Rename Subset...
+    .ss-content-model-space = Content cannot be placed into model space. Please switch to paper space and try again.
+    .ss-cannot-read = cannot be read
     .ss-rename-renumber-view = Rename & Renumber View
     .ss-list-of-blocks = List of Blocks
     .ss-select-block = Select Block