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>

docs/cadcodec-reader-gaps.md

@@ -7,8 +7,8 @@ reloading it, and comparing entity fields.
 **Status (23 September 2026):** the fixes landed in cadcodec as
 [#48](https://github.com/HakanSeven12/cadcodec/pull/48) (issues 1-6) and
 [#51](https://github.com/HakanSeven12/cadcodec/pull/51) (the first three style findings), and
-the block description with commit `dd1d7bf` (cadcodec issue #49). OCS pins `dd1d7bf`, and the
-canaries below were flipped against it. What is still open:
+the block description with commit `dd1d7bf` (cadcodec issue #49). OCS pins `d290dbe`, which
+includes it; the canaries below were flipped against `dd1d7bf`. What is still open:
 
 - **ATTDEF `lock_position`** (issue 1): the reader is complete, but the DXF writer emits no
   group 280 at all, neither the version byte nor the lock flag the reader expects after it.