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 <[email protected]>

src/scene/mod.rs

@@ -1268,21 +1268,15 @@ fn build_derived_caches_impl(
                 EntityType::Ole2Frame(ole) => ImageModel::from_ole2frame(ole).map(|m| (handle, m)),
                 EntityType::Underlay(u) => match doc.objects.get(&u.definition_handle) {
                     Some(acadrust::objects::ObjectType::UnderlayDefinition(def)) => {
-                        {
                         // Paper-space underlays adjust to the white sheet.
-                        let model = doc.objects.values().find_map(|object| match object {
-                            acadrust::objects::ObjectType::Layout(l) if l.name == "Model" => Some(l.block_record),
-                            _ => None,
-                        });
                         let owner = u.common.owner_handle;
-                        let background = if owner.is_null() || model.is_none_or(|m| m == owner) {
+                        let background = if owner.is_null() || owner == model_block {
                             LOAD_BG
                         } else {
                             [1.0, 1.0, 1.0, 1.0]
                         };
                         ImageModel::from_underlay(u, def, background).map(|m| (handle, m))
                     }
-                    }
                     _ => None,
                 },
                 _ => None,