Paste where the view shows it, editor offsets included (#263)

Paste mixed two frames. The pointer comes from the Scene View, which
draws every object moved by the editor offsets of it and its parents.
Paste turned that point into a local position through the parents'
plain world transform, so the copy landed beside the pointer by the
offset of the parent it went into. Without a pointer, an original with
an offset of its own had its copy placed beside its game position,
which the view does not show.

- A copied root now remembers where the view showed it
  (`ClipRoot.shown`, from `editorTransform`) instead of its world
  position.
- New `editorLocalPositionFor` in `properties/transform.ts` turns a
  shown point into a local position through the parent chain with the
  editor offsets, as the view draws it. Paste uses it.
- The copy itself still gets no editor offset of its own, as since
  #240. In the game it stands where it was drawn, minus the offsets of
  its parents.
- Re-parenting under a parent with an offset still keeps the game
  position, so the object jumps in the view by that offset. That is a
  different rule from paste and is left as it is.

Tests:
- Unit (clipboard, groups, references, transform): 50 passed, 2 new.
- e2e 51 on melektaus-atx: ALL PASSED, 12 checks, 1 new (51f).
- Gate on melektaus-atx: 195 files, 2829 tests, CHECK EXIT 0.
- Counter-checks: without the paste fix both new unit tests fail
  (copy at 540/470 instead of 500/500) and 51f fails by exactly the
  60/-40 offset. With the root remembering its world position again,
  the own-offset unit test fails.
- No full run. The e2e total of 1591 is 1590 plus 1.

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

src/editor/clipboard.ts

@@ -123,8 +123,8 @@ function pasteParents(
 
 /**
  * Pastes the copied objects into `holderId`, into or beside `picked` – by default the one selected
- * object. With `pointer` (world units) the copy is centred on it, otherwise it lands a step beside
- * the original, a step further for every earlier paste still there.
+ * object. With `pointer` (world units as the view shows them) the copy is centred on it, otherwise
+ * it lands a step beside the original, a step further for every earlier paste still there.
  */
 export function pasteObjects(
   state: EditorState,
@@ -141,7 +141,7 @@ export function pasteObjects(
     pointer &&
     centredOn(
       pointer,
-      clip.roots.map((r) => ({ x: r.world.x, y: r.world.y, w: 0, h: 0 })),
+      clip.roots.map((r) => ({ x: r.shown.x, y: r.shown.y, w: 0, h: 0 })),
     );
   const shift = centred
     ? { x: Math.round(centred.x), y: Math.round(centred.y) }