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>

tools/e2e/51-clipboard.mjs

@@ -105,6 +105,24 @@ export async function clipboard(t) {
     JSON.stringify({ target, rows, inside }),
   );
   await undo();
+
+  // 51f. The red crate drawn aside by its editor offset (#263): Ctrl+V with it selected puts the
+  //      copy inside it and still right under the pointer, where the view shows the copy.
+  await t.mutate(`
+    __gm.state.activeScene.objects.find((o) => o.id === ${JSON.stringify(RED)}).editorOffset = { x: 60, y: -40 }`);
+  await select({ kind: 'object', holderId: 'scene1', objectId: RED, objectIds: [RED] });
+  const offsetSpot = await json('__gm.emptySpot()');
+  await moveTo(offsetSpot);
+  await press('v', { ctrl: true });
+  const underRedId = (await selected()).objectId;
+  const underRed = (await stored()).find((o) => o.id === underRedId);
+  const shownAt = await json(`__gm.objectScreen(${JSON.stringify(underRedId)})`);
+  check(
+    'Ctrl+V into a parent with an editor offset still lands under the pointer',
+    underRed?.assetId === 'crate' && underRed.parentId === RED && near(shownAt, offsetSpot),
+    JSON.stringify({ offsetSpot, shownAt, underRed: underRed && underRed.position }),
+  );
+  await undo();
   check('the scene is back as it was', (await stored()).length === before.length);
 
   // 51d. A node of the Mover behavior, copied and pasted under the pointer in its own graph.