#1002: new art is refused when no layer is shown and unlocked

With every layer hidden or locked, the insertion layer fell back to the top layer anyway, so
drawing a shape, typing, pasting, making a graph, a flare, a grid, trim marks or a symbol put
the art on a hidden or locked layer: invisible, or unselectable by Select All. Illustrator
refuses to draw on a locked or hidden target layer (public forum answers, e.g.
https://community.adobe.com/t5/illustrator/can-t-draw-a-new-object-in-my-document/m-p/11107182).

DocState::target_parent is insertion_parent for new art, failing with "the target layer is
locked or hidden" when it would be a layer that isn't editable; those creation paths use it.
Another layer that is shown and unlocked still takes the art, as before. The message is in the
de, es, fr, it, ja, ru and uk catalogs. File > Place is left as it is (another branch reworks
it).

The test hides, then locks, the only layer: an ellipse, a polar grid, text and a paste each
fail with the message and leave the document unchanged; a new layer then takes a rectangle.

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

# Conflicts:
#	ROADMAP.md

crates/engine/src/cmd/edit.rs

@@ -346,7 +346,7 @@ fn paste_clip(s: &mut Session, p: &Value, mode: PasteMode, clip: &Clipboard, cho
     let off = s.prefs.paste_offset;
     let st = s.doc()?;
     let same_doc = clip.source_doc == Some(st.uid);
-    let parent = st.insertion_parent();
+    let parent = st.target_parent()?;
     // A copied artboard comes back with its art: right of the last artboard, or where it was
     // (Paste in Place, in Front, in Back). Paste on All Artboards pastes only the art.
     let board = clip