Point clouds: PCEXTRACTEDGE, PCEXTRACTCORNER, PCEXTRACTCENTERLINE, PCEXTRACTSECTION

Planes are found from the cloud points under the pick and grown over
the connected points on them: two planes give a line along their
intersection over the points' extent, three a point at their corner.
A cylindrical segment gives a line along its axis. A live section
object traces the points on its kept side as polylines or lines in the
section plane, with a preview and Accept/Settings/Undo;
-PCEXTRACTSECTION creates them directly.

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

src/modules/insert/mod.rs

@@ -18,6 +18,7 @@ mod mview_block;
 mod open_obj;
 pub(crate) mod pc_attach;
 pub(crate) mod pc_crop;
+pub(crate) mod pc_extract;
 pub(crate) mod pc_stylize;
 pub(crate) mod pdf_attach;
 pub(crate) mod pdf_clip;