Add a Get world position node with just the world x and y

Get position hands out four numbers, local and world. A graph that
only needs where an object is in the world had to pick the two world
ports out of four and leave the local ones dangling.

- Get world position has one object input and the outputs x and y.
  It reads the same worldPositionOf as Get position, so a child adds
  every parent's position in.
- Without an object it reports the origin, like Get position.

Tests:
- Node catalog: a top-level object, a child under a parent and no
  object (3 cases).
- node-catalog and hierarchy: 2 files, 378 tests, all green. The
  full gate was not run for this commit, CI covers it.

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

tests/core/node-catalog.test.ts

@@ -752,6 +752,19 @@ const CASES: Record<string, Case[]> = {
       outputs: { x: 0, y: 0, worldX: 0, worldY: 0 },
     },
   ],
+  GetWorldPosition: [
+    {
+      name: 'a top-level object is at its own position',
+      inputs: { object: at('A', 10, 20) },
+      outputs: { x: 10, y: 20 },
+    },
+    {
+      name: 'a child is at the summed position of its parents',
+      inputs: { object: { ...at('child', 10, 20), parent: at('parent', 100, 200) } },
+      outputs: { x: 110, y: 220 },
+    },
+    { name: 'no object is the origin', inputs: { object: null }, outputs: { x: 0, y: 0 } },
+  ],
   GetZ: [
     {
       name: 'a child reports its own z and the z summed up with its parents',