Let the places of a song share what it keeps to itself (#357)

With clips, one take serves many items: four items on the four clips
of one take. The rule from #355 gave every further place its own copy
of an embedded asset, so a cut made in the Sound tab reached one item
only. Now the song, its tracks and its items share a sound, a pattern
or a sound FX the song keeps.

- settleEmbedded no longer copies within the song. An embedded asset
  stays as long as one place names it, and goes with the last one.
- A paste from another song still gets a copy, but one copy for all
  the places naming the same asset, with its clip ids mapped.
- The picks in a song offer what the song keeps, under a line after
  the project's assets: the Sound row of an item the song's sounds
  and their clips, the Pattern row its patterns, every sound FX pick
  its sound FX.
- Make project asset and Embed a copy are unchanged.

The project cbbf160bb7e8 was merged by hand afterwards: the items of
Song 2 on three copies of Take 1 now play the same clips of the first
one, and the copies are gone.

Tests:
- Unit embedded, sound-clips, own-fx and the song tests: 66 green,
  3 counter-checks red as expected
- e2e 65 on melektaus-atx: ALL PASSED, 52 checks
- Gate on melektaus-atx: CHECK EXIT 0, 271 files, 4198 tests

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

tests/editor/own-fx.test.ts

@@ -77,6 +77,18 @@ describe('a sound FX of its own in a song (#355)', () => {
     expect(embeddedIn(state.project, songId).map((a) => a.name)).toEqual(['Sound FX 2']);
   });
 
+  it('is offered to every place of its song, which share it (#357)', () => {
+    const { state, songId, theme, track, onTrack, onItem } = setup();
+    const id = createOwnFx(state, songId, onTrack)!;
+    const entries = ownFxEntries(state, songId, '', onItem);
+    expect(labels(entries)).toEqual(['• Sound FX 1', 'Create sound FX']);
+    const own = entries.find((e) => 'label' in e && e.label === '• Sound FX 1');
+    if (own && 'onSelect' in own) own.onSelect();
+    expect([track().fx, theme().items[0]!.fx]).toEqual([id, id]);
+    state.execute(onTrack(''));
+    expect(findAsset(state.project, id)?.owner).toBe(songId);
+  });
+
   it('goes when its track picks another one, and comes back on undo', () => {
     const { state, songId, track, echoId, onTrack } = setup();
     const id = createOwnFx(state, songId, onTrack)!;