fix(video-workflows): pad the frame's own duration to match the transition tail (#1889)

* fix(video-workflows): pad the frame's own duration to match the transition tail

transitions.mjs extends the index.html WRAPPER's data-duration to cover an
outgoing transition's tail, but the frame's own internal composition file
kept its shorter, content-only data-duration (authored per frame-worker.md's
"duration is fixed upstream" instruction). The render engine clip-gates a
sub-composition's visible content at its own declared duration, so content
vanished abruptly at content-end instead of fading through the wrapper's
extended fade-out tween.

A user root-caused and verified this themselves: padding the frame's own
duration to match the wrapper fixed it, project-wide, across every
non-final frame. transitions.mjs already computes the correct padded
duration for the wrapper - it now writes the same value into the matching
frame's own file at inject time.

Extracted to a shared lib/pad-frame-duration.mjs (mirroring the existing
lib/transition-registry.mjs convention) since transitions.mjs's own
top-level CLI dispatch runs on import, making it untestable directly.
Duplicated identically across pr-to-video, faceless-explainer, and
product-launch-video, whose transitions.mjs copies are otherwise
byte-identical (confirmed via diff) - one root cause, one fix, applied
everywhere it lives.

* fix(skills): avoid duration helper file race

skills/product-launch-video/scripts/transitions.mjs

@@ -28,6 +28,7 @@ import { join, resolve } from "node:path";
 import { parseStoryboard } from "./lib/storyboard.mjs";
 import { parseFormat } from "./lib/dimensions.mjs";
 import { loadTransitionRegistry, transitionsByName } from "./lib/transition-registry.mjs";
+import { padFrameInternalDuration } from "./lib/pad-frame-duration.mjs";
 
 const flag = (argv, name, def) => {
   const i = argv.indexOf(`--${name}`);
@@ -183,6 +184,12 @@ function runInject(argv) {
     const dur = resolveDur(spec, rec, reg);
     const T = r3(incoming.start); // cut = incoming start (frames tile)
     outgoing.duration = r3(outgoing.duration + dur); // extend outgoing only
+    padFrameInternalDuration(
+      hyperframesDir,
+      order[i - 1].frame.src,
+      outgoing.id,
+      outgoing.duration,
+    );
     gsapLines.push(
       ...buildGsap(rec, outgoing.id, incoming.id, dur, T, spec.direction, CW, CH, die),
     );