fix(pipeline): trim picture-lock handles at the footage comp, not the template's SHOT layer

Manipulating startTime/outPoint on previewComp's SHOT layer touched a
comp duplicated from the artist-authored template, whose slate/shot
timing relationship the build script doesn't own -- and it dropped the
slate frame in production. The trim now happens one level down, on the
private single-layer footage precomp this script fully controls;
previewComp's own sizing logic is untouched from before this feature
existed, since it already generalizes correctly to any shotComp
duration.

Also threads the picture-lock skip reason through to the export's
timeline, so a shot missing sequence timecodes or a matching picture
lock file is visible without digging into worker-machine logs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

RenderWorker/VFXReviewWorker/JobExecutor.cs

@@ -461,6 +461,7 @@ public sealed class JobExecutor
                     ["thumbnailKey"] = thumbKey,
                     ["piclockRefKey"] = piclockRefKey,
                 },
+                ["piclockSkippedReason"] = result.Build?.PiclockSkippedReason,
                 ["renderStats"] = new Dictionary<string, object?>
                 {
                     ["previewSeconds"] = (int)result.Seconds,