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/io/mod.rs

@@ -4,9 +4,11 @@
 // Default save format: DWG (AC1032 / R2018+).
 
 pub mod file_association;
+pub mod font_repo;
 #[cfg(not(target_arch = "wasm32"))]
 pub mod edit_lock;
 pub mod obj;
+pub mod ole_embed;
 #[cfg(not(target_arch = "wasm32"))]
 pub mod single_instance;
 pub mod pdf_export;
@@ -1554,6 +1556,23 @@ pub async fn pick_image_file() -> Result<(PathBuf, u32, u32), String> {
     Ok((path, w, h))
 }
 
+/// Pick an image file and prepare it for embedding (IMAGEEMBED). The bytes
+/// are read before returning so the OLE2FRAME payload is ready to place.
+pub async fn pick_embedded_image_file() -> Result<ole_embed::EmbeddedImage, String> {
+    let handle = crate::sys::file_dialog()
+        .set_title(crate::t!("Select Image File").as_ref())
+        .add_filter(crate::t!("Images").as_ref(), &["png", "jpg", "jpeg", "bmp", "tiff", "tif"])
+        .add_filter(crate::t!("PNG").as_ref(), &["png"])
+        .add_filter(crate::t!("JPEG").as_ref(), &["jpg", "jpeg"])
+        .add_filter(crate::t!("All Files").as_ref(), &["*"])
+        .pick_file()
+        .await
+        .ok_or_else(|| "Cancelled".to_string())?;
+    let name = handle.file_name();
+    let bytes = handle.read().await;
+    ole_embed::EmbeddedImage::from_bytes(name, bytes)
+}
+
 /// Save `doc` to `path` with the given DXF version, overriding `doc.version`.
 /// Format is auto-detected from the extension (dwg / dxf).
 pub fn save_as_version(