fix(producer): derive duration from sub-composition timing when root has no data-duration

When the root element lacks an explicit data-duration attribute and
there is no GSAP timeline, getDeclaredDuration now computes
max(data-start + data-duration) across all sub-compositions instead
of returning zero.

Author: miguel-heygen

packages/producer/src/services/fileServer.ts

@@ -474,7 +474,15 @@ const HF_BRIDGE_SCRIPT = `(function() {
     var root = document.querySelector('[data-composition-id]');
     if (!root) return 0;
     var d = Number(root.getAttribute('data-duration'));
-    return Number.isFinite(d) && d > 0 ? d : 0;
+    if (Number.isFinite(d) && d > 0) return d;
+    var comps = document.querySelectorAll('[data-composition-src]');
+    var maxEnd = 0;
+    for (var i = 0; i < comps.length; i++) {
+      var start = Number(comps[i].getAttribute('data-start')) || 0;
+      var dur = Number(comps[i].getAttribute('data-duration')) || 0;
+      if (dur > 0) maxEnd = Math.max(maxEnd, start + dur);
+    }
+    return maxEnd;
   }
   function seekSameOriginChildFrames(frameWindow, nextTimeMs) {
     var frames;