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/scene/model/pdf_raster.rs

@@ -18,7 +18,7 @@ pub struct PdfPage {
 
 const RASTER_DPI: f32 = 150.0;
 
-type PageKey = (String, String);
+type PageKey = (String, String, u32);
 
 fn page_cache() -> &'static Mutex<HashMap<PageKey, Option<Arc<PdfPage>>>> {
     static CACHE: OnceLock<Mutex<HashMap<PageKey, Option<Arc<PdfPage>>>>> = OnceLock::new();
@@ -40,12 +40,18 @@ pub fn register_source(path: &str, bytes: Arc<Vec<u8>>) {
     page_cache()
         .lock()
         .unwrap_or_else(|error| error.into_inner())
-        .retain(|(cached_path, _), _| cached_path != path);
+        .retain(|(cached_path, _, _), _| cached_path != path);
 }
 
 /// Rasterise a 1-based PDF page, memoised by source path and page name.
 pub fn rasterize_page(path: &str, page: &str) -> Option<Arc<PdfPage>> {
-    let key = (path.to_string(), page.to_string());
+    rasterize_page_at_dpi(path, page, RASTER_DPI)
+}
+
+/// Rasterise a 1-based PDF page at a caller-chosen DPI, memoised per source
+/// path, page and DPI (print quality differs from the on-screen 150 DPI).
+pub fn rasterize_page_at_dpi(path: &str, page: &str, dpi: f32) -> Option<Arc<PdfPage>> {
+    let key = (path.to_string(), page.to_string(), dpi.to_bits());
     if let Some(hit) = page_cache()
         .lock()
         .unwrap_or_else(|error| error.into_inner())
@@ -55,7 +61,7 @@ pub fn rasterize_page(path: &str, page: &str) -> Option<Arc<PdfPage>> {
         return hit;
     }
 
-    let built = rasterize_uncached(path, page);
+    let built = rasterize_uncached(path, page, dpi);
     page_cache()
         .lock()
         .unwrap_or_else(|error| error.into_inner())
@@ -63,12 +69,12 @@ pub fn rasterize_page(path: &str, page: &str) -> Option<Arc<PdfPage>> {
     built
 }
 
-fn rasterize_uncached(path: &str, page: &str) -> Option<Arc<PdfPage>> {
+fn rasterize_uncached(path: &str, page: &str, dpi: f32) -> Option<Arc<PdfPage>> {
     let bytes = source_bytes(path)?;
     let pdf = Pdf::new(bytes).ok()?;
     let page_no = page.trim().parse::<usize>().unwrap_or(1).max(1);
     let page = pdf.pages().get(page_no - 1)?;
-    let scale = RASTER_DPI / 72.0;
+    let scale = dpi / 72.0;
     let pixmap = hayro::render(
         page,
         &RenderCache::new(),
@@ -86,7 +92,7 @@ fn rasterize_uncached(path: &str, page: &str) -> Option<Arc<PdfPage>> {
         pixels: Arc::new(pixmap.data_as_u8_slice().to_vec()),
         width,
         height,
-        dpi: RASTER_DPI,
+        dpi,
     }))
 }