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/commands/draw.rs

@@ -57,6 +57,10 @@ impl OpenCADStudio {
                 return Some(Task::done(Message::ImagePick));
             }
 
+            cmd if cmd == "IMAGEEMBED" => {
+                return Some(Task::done(Message::ImageEmbedPick));
+            }
+
             "REVCLOUD" | "REVCLOUD_RECTANGULAR" | "REVCLOUD_POLYGONAL" | "REVCLOUD_FREEHAND" => {
                 use crate::modules::draw::draw::revcloud::RevCloudCommand;
                 let view_height = self.tabs[i].scene.camera.borrow().ortho_size() as f64 * 2.0;

src/app/commands/mod.rs

@@ -622,6 +622,7 @@ inventory::submit!(crate::command::CommandRegistration {
         "IM",
         "IMAGE",
         "IMAGEATTACH",
+        "IMAGEEMBED",
         "IMPORTOBJ",
         "ISOLATEOBJECTS",
         "LA",