feat: plot a model-space window to PDF

Pick a rectangular window in model space with the existing PLOTWINDOW command (now enabled in model space, previously paper-space only) and export it to a PDF at a chosen ISO paper size (A4-A0), orientation and scale (fit or ratio). The window is a hard clip boundary. Adds paper-size presets, a window-to-sheet transform, scale + clip support in the PDF exporter, and Page Setup controls (format/orientation/pick window).

src/app/commands/display.rs

@@ -509,13 +509,11 @@ impl OpenCADStudio {
                 }
             }
 
+            // Model space now has its own dialog section (window-plot format /
+            // orientation / pick), so PAGESETUP opens there too, not just on
+            // paper-space layouts.
             "PAGESETUP" => {
-                if self.tabs[i].scene.current_layout == "Model" {
-                    self.command_line
-                        .push_error("PAGESETUP: switch to a paper space layout first.");
-                } else {
-                    return Some(Task::done(Message::PageSetupOpen));
-                }
+                return Some(Task::done(Message::PageSetupOpen));
             }
 
             // ── Recognized commands whose full implementation is pending ─────────