PDFIMPORTIMAGEPATH and per-import layer prefixes

- PDFIMPORTIMAGEPATH names the image extraction folder: relative to the
  PDF's folder (default "PDF Images"), absolute as given, "." for none.
- Every import of the session gets the next prefix (PDF_, PDF2_, PDF3_ ...),
  also when the same file is imported again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/commands/styleprops.rs

@@ -1022,6 +1022,7 @@ impl OpenCADStudio {
                     | "PDFIMPORTMODE"
                     | "PDFIMPORTFILTER"
                     | "PDFIMPORTLAYERS"
+                    | "PDFIMPORTIMAGEPATH"
                     | "XDWGFADECTL"
                     | "POINTCLOUDCLIPFRAME"
                     | "XCLIPFRAME"
@@ -1158,6 +1159,24 @@ impl OpenCADStudio {
                         }
                         return Some(self.finish_dispatch(cmd));
                     }
+                    // A folder name; "." clears it.
+                    if name == "PDFIMPORTIMAGEPATH" {
+                        use crate::modules::insert::pdf_import::{image_path, set_image_path};
+                        match &value {
+                            Some(value) => {
+                                let value = value.trim().trim_matches('"');
+                                set_image_path(if value == "." { String::new() } else { value.to_string() });
+                            }
+                            None => {
+                                self.command_line.push_output(&format!(
+                                    "Enter new value for PDFIMPORTIMAGEPATH, or . for none <\"{}\">:",
+                                    image_path()
+                                ));
+                                self.pending_setvar = Some(name.clone());
+                            }
+                        }
+                        return Some(self.finish_dispatch(cmd));
+                    }
                     if matches!(name.as_str(), "PDFOSNAP" | "UOSNAP") {
                         let current = i16::from(crate::scene::model::pdf_vector::pdf_osnap());
                         if let Some(value) = &value {