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/meta.json

@@ -0,0 +1,16 @@
+{
+  "name": "Distributed: Three.js WebGL boundary",
+  "description": "2s composition (20 frames @ 10fps) with a Three.js purple cube on a dark background. Validates that the GSAP batching proxy correctly forwards WebGL render callbacks and that CDP screenshot capture composites WebGL canvas layers — catches the v0.6.80 regression where the plain-object proxy silently dropped eventCallback() and other non-allowlisted GSAP methods, producing black frames.",
+  "tags": ["distributed", "threejs", "webgl"],
+
+  "minPsnr": 25,
+  "maxFrameFailures": 0,
+
+  "minAudioCorrelation": 0.9,
+  "maxAudioLagWindows": 120,
+
+  "renderConfig": {
+    "fps": 10,
+    "chunkSize": 10
+  }
+}

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