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/mcp.rs

@@ -54,6 +54,7 @@ const EXECUTE_OPS: &[&str] = &[
     "property",
     "set_properties",
     "action",
+    "embed_image",
     "save",
     "stop",
     "batch",
@@ -72,6 +73,7 @@ const BATCH_STEP_OPS: &[&str] = &[
     "property",
     "set_properties",
     "action",
+    "embed_image",
     "save",
     "stop",
 ];
@@ -717,6 +719,12 @@ fn validate_execute_request(request: &Value, op: &str) -> Result<(), String> {
             )),
             None => missing("name", r#"{"op":"action","name":"zoom_extents"}"#),
         },
+        "embed_image" if request["path"].as_str().is_none_or(str::is_empty) => {
+            missing(
+                "path",
+                r#"{"op":"embed_image","path":"/path/logo.png","at":[0,0,0],"width":100}"#,
+            )
+        }
         _ => Ok(()),
     }
 }
@@ -902,7 +910,9 @@ fn execute_request_schema() -> Value {
             "camera_revision":{"type":"integer","minimum":0,"description":"Expected camera revision when view state matters."},
             "selection":{"type":"array","items":handle.clone(),"description":"Expected selected handles from current state."},
             "cmd":{"type":"string","minLength":1,"description":"Command name followed by its prompt answers separated by spaces. Points use x,y or x,y,z; option answers use their token. Read command details first when unsure.","examples":["LINE 0,0 10,10","CIRCLE 5,5 3","PLINE 0,0 10,0 10,10 C"]},
-            "path":{"type":"string","minLength":1,"description":"Absolute drawing path for open or save."},
+            "path":{"type":"string","minLength":1,"description":"Absolute path: drawing for open or save, image file for embed_image."},
+            "at":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"World [x,y] or [x,y,z] placement corner for embed_image (picture grows up-right)."},
+            "width":{"type":"number","exclusiveMinimum":0,"description":"World width for embed_image; height follows the image aspect ratio. Defaults to pixel_width/100."},
             "kind":{"type":"string","enum":["text","token","point","entity","structure","selection","enter"],"description":"Input kind listed in state.command.accepts."},
             "text":{"type":"string","description":"Free text or one option/value token."},
             "point":point,
@@ -943,6 +953,7 @@ fn execute_request_schema() -> Value {
             {"properties":{"op":{"const":"property"}},"required":["field","value"]},
             {"properties":{"op":{"const":"set_properties"}},"required":["collection","updates"]},
             {"properties":{"op":{"const":"action"}},"required":["name"]},
+            {"properties":{"op":{"const":"embed_image"}},"required":["path"]},
             {"properties":{"op":{"const":"save"}}},
             {"properties":{"op":{"const":"stop"}}},
             {"properties":{"op":{"const":"batch"}},"required":["steps"]}