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/control/mod.rs

@@ -781,6 +781,8 @@ impl OpenCADStudio {
             "set_properties" => self.control_set_record_properties(req)?,
             "action" => self.control_ui_action(req)?,
             #[cfg(not(target_arch = "wasm32"))]
+            "embed_image" => self.control_embed_image(req)?,
+            #[cfg(not(target_arch = "wasm32"))]
             "save" => {
                 let path = req["path"]
                     .as_str()
@@ -1387,4 +1389,40 @@ mod tests {
         );
         let _ = std::fs::remove_file(path);
     }
+
+    #[test]
+    fn embed_image_op_places_an_ole2frame_and_undoes_it() {
+        let mut app = OpenCADStudio::new_for_test();
+        request(&mut app, json!({"op":"new"}));
+        let img = image::RgbaImage::from_pixel(40, 30, image::Rgba([9, 9, 9, 255]));
+        let path = std::env::temp_dir().join(format!("ocs-embed-{}.png", session_id()));
+        img.save(&path).unwrap();
+
+        let response = request(
+            &mut app,
+            json!({"op":"embed_image","path":path.to_string_lossy(),"at":[0,0,0],"width":20}),
+        );
+        assert_eq!(response["status"], "completed", "{response}");
+        let handle = response["result"]["handle"].as_str().unwrap().to_string();
+        assert_eq!(response["result"]["kind"], "Ole2Frame");
+        let ole_count = |app: &OpenCADStudio| {
+            app.tabs[app.active_tab]
+                .scene
+                .document
+                .entities()
+                .filter(|e| matches!(e, acadrust::EntityType::Ole2Frame(_)))
+                .count()
+        };
+        assert_eq!(ole_count(&app), 1);
+
+        // The entity must be queryable like any other and undoable as one step.
+        let queried =
+            app.automation_op(json!({"op":"entities","type":"OLE2FRAME"}).to_string().as_str());
+        assert_eq!(queried["total"], 1, "{queried}");
+        request(&mut app, json!({"op":"undo"}));
+        assert_eq!(ole_count(&app), 0);
+        let _ = std::fs::remove_file(path);
+        let _ = handle;
+    }
 }
+