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/view/modal.rs

@@ -53,6 +53,7 @@ impl OpenCADStudio {
             Some(K::AttributeEditor) => crate::tr!("modal", "attribute-editor"),
             Some(K::SaveDialog) => crate::tr!("modal", "save-drawing-as"),
             Some(K::Recovery) => crate::tr!("modal", "recovery-report"),
+            Some(K::MissingFonts) => crate::t!("Missing fonts").into_owned(),
             Some(K::RecoveryPrompt) => crate::tr!("modal", "recovery-prompt"),
             Some(K::GpuWarning) => crate::tr!("gpu", "title"),
             None => String::new(),
@@ -1568,6 +1569,17 @@ impl OpenCADStudio {
                     )
                 })
             }
+            super::super::ModalKind::MissingFonts => {
+                let fonts = self.missing_fonts.as_ref()?;
+                let font_source = &self.font_source_input;
+                automatic_flow(ex, |flow| {
+                    crate::ui::window::missing_fonts::view_window(
+                        fonts,
+                        &font_source,
+                        flow,
+                    )
+                })
+            }
             super::super::ModalKind::Recovery => {
                 let report = self.recovery_report.as_ref()?;
                 sized_flow(ex, 680, 460, |flow| {