fix(core): re-register hf-timelines-built listener in maybePublishRenderReady (#1279)

Compositions that defer gsap.timeline() registration past DOMContentLoaded
(via setTimeout, template instantiation, or dynamic script loading) hit a
race where __renderReady stays false forever:

1. At DOMContentLoaded, __hfTimelinesBuilding is false — init.ts skips
   the hf-timelines-built listener and sets __renderReady = true
2. The deferred script runs, calls gsap.timeline().to() which sets
   __hfTimelinesBuilding = true via the batching proxy
3. The deferred maybePublishRenderReady() sees building=true, sets
   __renderReady = false, but never registers a listener to retry
4. __renderReady stays false, __hf.duration returns 0, pollHfReady
   times out with "Composition has zero duration"

Fix: when maybePublishRenderReady encounters __hfTimelinesBuilding=true,
register a one-shot hf-timelines-built listener to retry — matching the
pattern already used at init time for the synchronous batching case.

Closes #1260

packages/producer/tests/distributed/three-boundary/output/output.mp4

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:cc8c784064e83a62324b4968ef71d3f9c5e151ccf9f3e96a725660bb6c9bb3b9
+size 22114