M10: Enhance scanned file reports scans inside Form XObjects and names JPEG 2000

- A scan drawn only through grouped Form artwork is reported in skipped
  (once per form, with every page that draws it) instead of being counted
  as no scan; a Form of vector artwork holding only a small picture
  (under 36 dpi over its area) still counts as no scan.
- decode_samples checks the filter before the colour space and bit depth,
  so a JPEG 2000 image without /ColorSpace or /BitsPerComponent is
  reported as JPEG 2000, not as a colour-space or bit-depth problem.
- Optimize and Enhance scanned file no longer start while the other runs:
  they share the progress card and capture the same document state.
- docs/gaps.md: background and edge-shadow removal apply to grey and RGB
  scans, despeckle also to 1-bit ones.

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

docs/gaps.md

@@ -165,8 +165,10 @@ update the numbers.
 ### 7. OCR reads only unaccented Latin
 
 - **Missing:** every other script and accented Latin; editable-text output; deskew, rotation,
-  despeckle and background clean-up as options of Recognize text (Enhance scanned file does them
-  on grey, RGB and 1-bit scans, not CMYK, indexed, JBIG2 or CCITT ones); MRC compression;
+  despeckle and background clean-up as options of Recognize text (Enhance scanned file removes
+  the background and edge shadows on grey and RGB scans and despeckles those and 1-bit ones; it
+  reports CMYK, indexed, JPEG 2000, JBIG2 and CCITT scans and scans drawn inside Form XObjects
+  and leaves them as they are); MRC compression;
   pluggable engines; OCR in the
   browser; scanner input.
 - **Evidence:** `ocr.ocr-languages` partial ("the models read only the Latin alphabet without