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/ui/window/plot.rs

@@ -160,6 +160,10 @@ pub struct PlotDialogState {
     pub upside_down: bool,
     pub copies: String,
     pub area: String,
+    /// The picked world-space plot window (x0, y0, x1, y1) backing
+    /// `area == "Window"`. Persisted so reopening the dialog — or the app —
+    /// keeps the same window instead of reporting an empty plot area.
+    pub window: Option<(f64, f64, f64, f64)>,
     pub center: bool,
     pub offset_x: String,
     pub offset_y: String,
@@ -219,6 +223,7 @@ impl Default for PlotDialogState {
             upside_down: false,
             copies: "1".into(),
             area: "Window".into(),
+            window: None,
             center: true,
             offset_x: "0.0".into(),
             offset_y: "0.0".into(),
@@ -263,6 +268,7 @@ impl PlotDialogState {
         self.upside_down = o.upside_down;
         self.copies = o.copies.clone();
         self.area = o.area.clone();
+        self.window = o.window;
         self.center = o.center;
         self.offset_x = o.offset_x.clone();
         self.offset_y = o.offset_y.clone();