Let a child sort with its parent so its Z stays local (#232)

An animated or set Z of -1 on a weapon put it behind everything on Z 0,
not just behind the player holding it. A child can now opt in to being
drawn at its parent's place, so its own Z only orders it against the
parent and its siblings.

- New property "Sort with parent" on sprites, texts and particle
  emitters, shown in the inspector right under Z. It is a normal
  property, set on the asset and overridable per object.
- With it on, the rest of the scene sees only the parent's Z and, where
  the layer sorts by Y, the parent's feet. Below 0 the child is drawn
  behind the parent, from 0 on in front.
- It works across levels: a grandchild with the switch hangs on the top
  object of the chain.
- It has no effect under a parent that is not drawn itself (container,
  behavior, camera, collider) or under a tilemap.
- New assets start with it on, saved ones read as off, so old projects
  draw unchanged. For that a schema row now has "initial" next to
  "default". The gold "changed" mark and reset follow "initial", so a
  fresh sprite is not marked as changed. No load migration is needed.
- parentGroups() in drawOrder.ts gives a slot only to the top of a
  chain and inserts the children there. Editor, play mode and picking
  all use it, so they agree.

Tests:
- 10 new unit tests in tests/viewport/sort-with-parent.test.ts.
- 8 existing tests list the sprite rows or defaults and got the row.
- New e2e check 5b-ii clicks the switch and checks order and undo.
- Counter-checks, all originals restored by cmp: switch ignored fails
  7, children not sorted by Z fails 6, no chain fails 1, "initial"
  ignored fails 9, row missing in the inspector fails e2e 5.
- ./check.sh: 166 files, 2426 tests, CHECK EXIT 0.
- e2e 5: ALL PASSED, 13 checks. Check total 1398, computed only.

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

src/editor/inspector/objectSection.ts

@@ -32,6 +32,7 @@ import {
   COMMON_PROPS,
   isCommonProp,
   isRowShown,
+  isSortProp,
   isTransformProp,
   type PropertyDef,
   schemaFor,
@@ -180,6 +181,9 @@ export function buildObjectSection(host: InspectorHost, holderId: string, object
         ),
     });
   }
+  // Right under Z, which it changes the meaning of.
+  for (const def of schemaForObject(project, asset, object).filter((d) => isSortProp(d.key)))
+    propertyRow(host, holderId, objectId, asset, def, resolved);
 
   // Turn, size and mirror sit with the position: together they are where the object is.
   const transform = schemaForObject(project, asset, object).filter((def) => isTransformProp(def.key));