fix(pdf): follow-ups to the PDF underlay merge

- Pin cadcodec upstream at d290dbe (the merged underlay change) and
  cadkernel at 4134ae3, which follows it; drop the fork patch, move the
  plugin-API and web-worker crates and the Python plugin lock to the same
  codec so one copy is built.
- "Import as block" with raster images left IMAGE entities without an
  image definition: block definition now creates it like add_entity does,
  through one shared helper.
- The three preview outlines (attach frame, clip boundary, import area)
  stay f64 instead of casting world points to f32.
- Page size / total / PDF scale entries use the catalog's positional
  placeholder; the bare {name} form failed to format in 20 locales.
- The Underlay Layers bulb is the SVG layer icon, not a text glyph.
- PDF dialogs use the shared dialog buttons and radios.
- Options opened from a PDF dialog clears its saved state on return.
- Paper-space underlay background reuses the model block handle already
  resolved; dead `let _ = i` lines and a misplaced doc comment removed.

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

src/app/update/mod.rs

@@ -137,6 +137,8 @@ impl OpenCADStudio {
         // Options opened from a PDF dialog returns to it.
         if self.active_modal == Some(Options) {
             if let Some(parent) = self.options_parent.take() {
+                self.options_saved = None;
+                self.options_close_confirm = false;
                 self.active_modal = Some(parent);
                 return;
             }
@@ -1326,9 +1328,7 @@ impl OpenCADStudio {
             ),
 
             Message::PdfAttachPickResult(Ok((path, bytes))) => {
-                let i = self.active_tab;
                 let path_str = path.to_string_lossy().into_owned();
-                let _ = i;
                 crate::scene::model::pdf_raster::register_source(&path_str, bytes);
                 // Pages, placement and path type are chosen in the Attach
                 // dialog; the definition is created with the underlay.
@@ -1355,9 +1355,7 @@ impl OpenCADStudio {
                 Message::PdfImportPickResult,
             ),
             Message::PdfImportPickResult(Ok((path, bytes))) => {
-                let i = self.active_tab;
                 let path_str = path.to_string_lossy().into_owned();
-                let _ = i;
                 crate::scene::model::pdf_raster::register_source(&path_str, bytes);
                 self.open_pdf_import_file(&path_str);
                 Task::none()