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/update/mod.rs

@@ -831,6 +831,14 @@ impl OpenCADStudio {
                 self.tabs[i].scene.selection.borrow_mut().context_menu = None;
                 // Any command also dismisses the Isolate action menu.
                 self.isolate_popup_open = false;
+                // "Pick window" (PLOTWINDOW) from Page Setup needs the backdrop
+                // gone so the viewport pick lands; every other command leaves an
+                // open modal (and its staged edits) untouched.
+                if cmd.trim().eq_ignore_ascii_case("PLOTWINDOW")
+                    || cmd.trim().eq_ignore_ascii_case("PW")
+                {
+                    self.close_active_modal();
+                }
                 self.dispatch_command(&cmd)
             }
 
@@ -2987,6 +2995,30 @@ impl OpenCADStudio {
             Message::PlotExportPath(None) => Task::none(),
             Message::PlotExportPath(Some(path)) => self.on_plot_export_path_some(path),
 
+            Message::PlotFormat(f) => {
+                self.plot_format = f;
+                Task::none()
+            }
+            Message::PlotOrientation(o) => {
+                self.plot_orientation = o;
+                Task::none()
+            }
+            Message::PlotWindowExport => {
+                let i = self.active_tab;
+                let stem = self.tabs[i]
+                    .current_path
+                    .as_deref()
+                    .and_then(|p: &std::path::Path| p.file_stem())
+                    .map(|s: &std::ffi::OsStr| s.to_string_lossy().into_owned())
+                    .unwrap_or_else(|| "drawing".into());
+                Task::perform(
+                    crate::io::pdf_export::pick_pdf_path_owned(stem),
+                    Message::PlotWindowExportPath,
+                )
+            }
+            Message::PlotWindowExportPath(None) => Task::none(),
+            Message::PlotWindowExportPath(Some(path)) => self.on_plot_window_export_path_some(path),
+
             // ── Print to system printer ───────────────────────────────────────
             Message::PrintToPrinter => self.on_print_to_printer(),
             Message::PrintResult(Ok(printer)) => {