feat: embed images (OLE2FRAME), print pipeline fixes, plot prefs, community fonts

- IMAGEEMBED: pack raster images into OLE2FRAME entities so a .dwg is
  self-contained; 'Embed Image' entry in the XREF attach menu; control/MCP
  op embed_image for external tools; dxf_name for OLE2FRAME queries.
- Scene: populate_images_from_document now rebuilds OLE2FRAME and PDF
  underlay models too (they used to vanish after any XREF op).
- Printing: add PRINTER_ENUM_NETWORK pass when listing printers; GDI
  spooler fallback (hayro raster at 300 DPI + StretchDIBits) for hosts
  whose PDF handler registers no print verb; DEVMODE orientation with a
  90-degree raster rotation fallback for v4 drivers; fix the fit-scale
  precedence bug that printed blank pages.
- PDF export dialogs on Windows use the async file dialog so the native
  overwrite confirmation no longer deadlocks the UI thread.
- Plot dialog: persist the chosen printer (saved on selection) and the
  picked plot window across sessions; page setups with no device no
  longer reset the output device.
- Community fonts: detect unresolvable .shx references on open and offer
  a download from the repository's fonts/ folder (contribution guide in
  fonts/README.md); custom font source URL setting for intranet font
  servers; downloaded fonts resolve from the per-user fonts directory.

src/app/command_driver.rs

@@ -4635,6 +4635,7 @@ impl OpenCADStudio {
                     let x1 = p1.x.max(p2.x);
                     let y1 = p1.y.max(p2.y);
                     self.plot_window = Some((x0, y0, x1, y1));
+                    self.plot_dialog.window = self.plot_window;
                     self.command_line.push_output(
                         crate::tf!("Plot window: {x0:.2},{y0:.2} to {x1:.2},{y1:.2}").as_ref(),
                     );
@@ -4642,6 +4643,8 @@ impl OpenCADStudio {
                     // receive the two clicks — bring the dialog back with the
                     // window now active.
                     self.plot_dialog.area = "Window".to_string();
+                    // Remember the pick immediately, like the printer choice.
+                    self.save_config();
                     self.active_modal = Some(super::ModalKind::Plot);
                 } else {
                     // PLOTWINDOW always describes the plotted layout. In MSPACE
@@ -4654,10 +4657,12 @@ impl OpenCADStudio {
                     let x2 = p1.x.max(p2.x);
                     let y2 = p1.y.max(p2.y);
                     self.plot_window = Some((x1, y1, x2, y2));
+                    self.plot_dialog.window = self.plot_window;
                     self.command_line.push_output(
                         crate::tf!("Plot window: {x1:.2},{y1:.2} to {x2:.2},{y2:.2}").as_ref(),
                     );
                     self.plot_dialog.area = "Window".to_string();
+                    self.save_config();
                     self.active_modal = Some(super::ModalKind::Plot);
                 }
                 self.tabs[i].active_cmd = None;