Let a container sort its content with its parent (#243)

A container is not drawn, so it had no place in the draw order. The
chain from its content to the parent of the container broke there, and
a container under a character could not be drawn together with it.

- A container gets the switch Sort with parent under Z. It defaults to
  off, also for new containers, so projects draw as they did.
- With the switch on, the whole content is drawn in the slot of the
  container's parent. The content's own switch does not count there.
- Containers in a row pass the content on as long as each has the
  switch on. On the top level or under a tilemap it has no effect.
- drawSlots follows the new sortsWith field of a draw item. Scene view,
  game and picking all use drawSlots, so all three agree.

Found on the way: a scene object hung directly under a container
spells the container out, and its template content is dropped. That is
the existing spelledOut rule, the tests now keep both cases apart.

Tests:
- ./check.sh: 178 files, 2573 tests, CHECK EXIT 0
- 7 new unit tests in sort-with-parent.test.ts: the switch, template
  content, override per container, a chain, top level and tilemap,
  game and picking
- e2e 5b-iii: a real click on the switch in the inspector, with undo
- 4 counter-probes over #242 and #243 bite (2 unit, 2 browser)

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

tools/e2e/05-drawing.mjs

@@ -85,6 +85,42 @@ export async function drawing(t) {
     objs.splice(objs.findIndex(o => o.id === 'o-sort'), 1);
     __gm.state.select(null)`);
 
+  // 5b-iii. A container sorted with its parent (#243): a container under o1 holds a crate on -1 in
+  //         its template, a third crate stands before o1. Off, as a new container starts, the crate
+  //         inside drops behind everything on 0; the container's own switch draws it right behind o1.
+  const INSIDE = 'o-cont~sort-in';
+  await mutate(`
+    const p = __gm.state.project;
+    const objs = __gm.state.activeScene.objects;
+    const make = (id, assetId, parentId, z) => ({ id, assetId, name: '', position: { x: 0, y: 0, z }, editorOffset: { x: 0, y: 0 }, overrides: {}, parentId, instanceEdits: {} });
+    p.assets.push({ id: 'sort-box', type: 'container', name: 'sort-box', props: { enabled: true }, objects: [make('sort-in', 'crate', '', -1)] });
+    objs.splice(objs.findIndex(o => o.id === 'o1'), 0, make('o-sort', 'crate', '', 0));
+    objs.push(make('o-cont', 'sort-box', 'o1', 0));`);
+  const boxOrder = () =>
+    json(`__gm.drawOrder().filter(id => ['o-sort', 'o1', ${JSON.stringify(INSIDE)}].includes(id))`);
+  const boxOff = await boxOrder();
+  await select({ kind: 'object', holderId: 'scene1', objectId: 'o-cont' });
+  const boxRow = await json("__gm.inspectorField('Sort with parent')");
+  if (boxRow) await click(boxRow.x, boxRow.y);
+  const boxOverride = (await object('o-cont')).overrides.sortWithParent;
+  const boxOn = await boxOrder();
+  await undo();
+  const boxUndone = await boxOrder();
+  check(
+    'Sort with parent on a container draws its content right behind the parent of the container, and undo takes it back',
+    JSON.stringify(boxOff) === `["${INSIDE}","o-sort","o1"]` &&
+      boxOverride === true &&
+      JSON.stringify(boxOn) === `["o-sort","${INSIDE}","o1"]` &&
+      JSON.stringify(boxUndone) === JSON.stringify(boxOff),
+    JSON.stringify({ boxRow, boxOff, boxOverride, boxOn, boxUndone }),
+  );
+  await mutate(`
+    const p = __gm.state.project;
+    const scene = __gm.state.activeScene;
+    scene.objects = scene.objects.filter(o => o.id !== 'o-sort' && o.id !== 'o-cont');
+    p.assets = p.assets.filter(a => a.id !== 'sort-box');
+    __gm.state.select(null)`);
+
   // 5c. The symbols are the asset panel's icons, white in a dark outline and without a plate
   //     behind them: one of each in a lane of its own, the pixels read on a grid over each icon
   //     (±12 world units round its centre). Each must show white and the outline, and none of the