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/missing_fonts.rs

@@ -0,0 +1,84 @@
+// Missing-fonts prompt — shown after a drawing opens with `.shx` fonts this
+// machine doesn't have. Offers to fetch them from the community repository
+// (see `fonts/README.md` in the repo root) instead of rendering with a
+// mismatched substitute.
+
+use crate::app::Message;
+use iced::widget::{button, column, container, row, scrollable, text, text_input, Space};
+use iced::{Element, Fill, Length, Shrink, Theme};
+
+fn muted_style(theme: &Theme) -> text::Style {
+    text::Style {
+        color: Some(theme.palette().background.weak.text),
+    }
+}
+
+/// The prompt: the missing-font list, a download action, and a skip.
+pub fn view_window<'a>(
+    fonts: &'a [String],
+    font_source: &'a str,
+    sizing: crate::ui::modal::ModalSizing,
+) -> Element<'a, Message> {
+    let content_width = if matches!(sizing.width, Length::Fill) {
+        Fill
+    } else {
+        Shrink
+    };
+    let content_height = if matches!(sizing.height, Length::Fill) {
+        Fill
+    } else {
+        Shrink
+    };
+    let listed: Vec<Element<'a, Message>> = fonts
+        .iter()
+        .map(|name| text(format!("  {name}")).size(12).into())
+        .collect();
+    let actions = row![
+        Space::new().width(content_width),
+        button(text(crate::t!("Skip")).size(12))
+            .on_press(Message::MissingFontsDismiss)
+            .style(button::secondary)
+            .padding([6, 14]),
+        button(text(crate::t!("Download")).size(12))
+            .on_press(Message::MissingFontsDownload)
+            .style(button::primary)
+            .padding([6, 14]),
+    ]
+    .spacing(8);
+
+    container(
+        column![
+            text(crate::t!("Missing fonts")).size(20),
+            text(crate::t!(
+                "This drawing uses fonts that are not installed on this machine. Download them from the OpenCADStudio community font repository?"
+            ))
+            .size(11)
+            .style(muted_style),
+            container(scrollable(column(listed).spacing(2)).height(content_height))
+                .padding([10, 12])
+                .width(content_width)
+                .height(content_height)
+                .style(container::bordered_box),
+            column![
+                text(crate::t!("Font source — leave empty for the community repository, or point at any folder (e.g. your company's font server):"))
+                    .size(10)
+                    .style(muted_style),
+                text_input(
+                    crate::t!("https://server/fonts or a GitHub raw folder").as_ref(),
+                    font_source,
+                )
+                .on_input(Message::MissingFontsSourceChanged)
+                .size(11)
+                .padding([4, 8])
+                .width(content_width),
+            ]
+            .spacing(3),
+            actions,
+        ]
+        .spacing(10)
+        .width(sizing.width)
+        .height(sizing.height),
+    )
+    .padding([12, 16])
+    .into()
+}