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/view/modal.rs

@@ -57,6 +57,8 @@ impl OpenCADStudio {
                     &self.page_setup_offset_y,
                     &self.page_setup_rotation,
                     &self.page_setup_scale,
+                    self.plot_format,
+                    self.plot_orientation,
                 ),
                 520,
                 460,