* 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
