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>

lib/render-pipeline/preview.ts

@@ -303,6 +303,8 @@ export interface FinalizeInput {
   };
   renderStats?: { renderSeconds?: number; previewSeconds?: number };
   media?: { width?: number; height?: number; frameCount?: number; fps?: number; fileName?: string };
+  /** Why the picture-lock trim/reference was skipped, when it was — surfaced on the export's timeline. */
+  piclockSkippedReason?: string | null;
 }
 
 /**
@@ -471,7 +473,12 @@ export async function finalizePreview(jobId: string, machineId: string, body: Fi
               ? " — review version media replaced"
               : ` — review version created (${inheritedApproval ?? "PENDING_REVIEW"})`
             : " — no preview media reported") +
-          (taskRenamed ? ` — task renamed to ${taskTitle}` : ""),
+          (taskRenamed ? ` — task renamed to ${taskTitle}` : "") +
+          (artifacts.piclockRefKey
+            ? " — picture-lock reference built"
+            : body.piclockSkippedReason
+              ? ` — picture lock skipped (${body.piclockSkippedReason})`
+              : ""),
       },
       {
         ...(versionId ? { versionId } : {}),