M3.6: opacity-mask editing mode — click the mask thumbnail to edit the mask art on a temporary isolated layer with any tool; the mask updates live after every edit; the object thumbnail (or transparency.stopEditingOpacityMask) leaves the mode

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

crates/engine/src/cmd/mod.rs

@@ -18,6 +18,7 @@ pub(crate) mod graph;
 pub mod help;
 mod layer;
 mod live;
+pub(crate) mod maskedit;
 pub(crate) mod menucmds;
 mod object;
 mod opacitymask;
@@ -167,6 +168,7 @@ pub fn command_specs() -> &'static [CommandSpec] {
         v.extend(graph::specs());
         v.extend(rasterfx::specs());
         v.extend(views::specs());
+        v.extend(maskedit::specs());
         v.extend(docmenu::specs());
         v.extend(docinfo::specs());
         v.extend(panelcmds::specs());