ADJUST: images and underlays, -IMAGEADJUST and PDF/DWF/DGNADJUST

ADJUST gathers raster images or PDF/DWF/DGN underlays (other objects are
dropped silently, pickfirst is used, a mixed set is refused), then asks the
image option (Brightness default) or the underlay option (last used), with
value prompts that offer the image's own value or the session's last
underlay fade/contrast, and Monochrome Yes/No. Invalid values re-prompt.
One undo step. -IMAGEADJUST, PDFADJUST, DWFADJUST and DGNADJUST take one
kind each. Raster image Brightness/Contrast/Fade move to an Image Adjust
section as whole numbers with 0-100 validation.

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

src/modules/insert/mod.rs

@@ -26,7 +26,7 @@ mod snap_underlays;
 pub(crate) mod solid3d_cmds;
 mod underlay_layers;
 pub(crate) mod wblock;
-mod xadjust;
+pub(crate) mod xadjust;
 pub(crate) mod xattach;
 pub(crate) mod xclip;
 pub(crate) mod xref_cmd;