fix(three-dissolve): expose window.__hf for capture engine readiness

The engine's initializeSession polls for window.__hf = { duration, seek }
to know the page is renderable. This was removed during the debug-globals
cleanup — the capture engine never saw readiness, polling until the 120s
CI timeout killed it, producing the HeadlessExperimental.beginFrame error.

Set __hf in both the onLoad and onError GLTF callbacks, alongside
the __tailwindReady resolution.

Author: miguel-heygen

registry/blocks/three-dissolve/three-dissolve.html

@@ -484,11 +484,13 @@
               );
               root.add(particlePoints);
               renderAt(lastRenderedTime);
+              window.__hf = { duration: DURATION, seek: renderAt };
               resolveReady();
             },
             undefined,
             (error) => {
               console.error("GLTF load failed:", error);
+              window.__hf = { duration: DURATION, seek: renderAt };
               resolveReady();
             },
           );