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/core/model/clipboard.ts

@@ -11,7 +11,7 @@ import {
   type GraphEdge,
   type GraphNode,
 } from '../graph/Graph';
-import { parentTransform, positionOf, worldTransform } from '../properties/transform';
+import { editorTransform, parentTransform, positionOf } from '../properties/transform';
 import { findObject, subtreeIds, subtreeRoots, treeOrder } from './hierarchy';
 import { isLiveInstance, isTemplateContent, resolvedHolder, splitInstanceId } from './instance';
 import type { Mat } from './matrix';
@@ -19,10 +19,13 @@ import type { Position } from './Properties';
 import type { ObjectHolder, Project } from './Project';
 import type { SceneObject } from './SceneObject';
 
-/** A copied subtree's top: where it stood in the world and the frame its own rows were meant in. */
+/**
+ * A copied subtree's top: where the editor showed it, editor offsets included (#263), and the
+ * frame its own rows were meant in.
+ */
 export interface ClipRoot {
   id: string;
-  world: Position;
+  shown: Position;
   parentMatrix: Mat;
 }
 
@@ -80,7 +83,7 @@ export function copyObjects(
       const object = findObject(view, id)!;
       return {
         id,
-        world: positionOf(worldTransform(project, view, object)),
+        shown: positionOf(editorTransform(project, view, object)),
         parentMatrix: parentTransform(project, view, object.parentId).m,
       };
     }),