fix(worker): stop PrepareOutputDir deleting the version's preview MOV/MP4

PrepareOutputDir cleared every file in the output dir whose name started
with the output pattern's prefix. The preview stage writes its MOV and MP4
into that same folder from the same basename ({outputDir}/{base}.mov), so
they matched the prefix and were deleted before aerender started.

The dir is not private to one export: outputDir is keyed on the shot's
manually-set shotVersion, not on the export, so re-queuing without a
Version Up renders into the folder again. That is exactly the "No preview"
workflow - export scaled, reverse the scale, re-render only the EXRs and
inherit the earlier MOV - and inheritPreviewMedia then handed the new
export a deliveryMovPath pointing at the file the render had just removed.
Nothing surfaced it: the review MP4 is an uploaded blob and still played,
and DeliveryStage treats a missing MOV as non-fatal, so the package
silently shipped EXRs with no viewing copy.

Match on prefix and extension instead, via a new
SequencePattern.MatchesOutputFile - the predicate ValidationStage and
DeliveryStage already applied inline. Crashed-attempt cleanup is unchanged;
only files with a different extension are now spared.

JobExecutor's post-render stats loop matched on prefix alone too. With the
media no longer deleted it would have counted the MOV/MP4 as frames and
failed validation's file_count check, so it uses the same matcher.

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

RenderWorker/VFXReviewWorker/JobExecutor.cs

@@ -76,12 +76,15 @@ public sealed class JobExecutor
             {
                 long totalBytes = 0;
                 int fileCount = 0;
-                var prefix = AerenderRunner.OutputPatternPrefix(manifest.OutputPattern);
+                // Prefix and extension both: the preview MOV/MP4 for this
+                // version share the basename and live in this same folder, and
+                // counting them as frames would inflate the EXR stats.
+                var pattern = SequencePattern.FromOutputPattern(manifest.OutputPattern);
                 try
                 {
                     foreach (var f in Directory.EnumerateFiles(outputDirLocal))
                     {
-                        if (!Path.GetFileName(f).StartsWith(prefix, StringComparison.OrdinalIgnoreCase)) continue;
+                        if (!pattern.MatchesOutputFile(Path.GetFileName(f))) continue;
                         fileCount++;
                         totalBytes += new FileInfo(f).Length;
                     }
@@ -94,8 +97,8 @@ public sealed class JobExecutor
                     // range, template mismatch, silently swallowed error).
                     // Until Phase 3 validation exists, an empty output dir must
                     // never become READY_FOR_QC.
-                    _log.LogError("Job {JobId}: aerender exited 0 but no \"{Prefix}*\" files exist in {Dir} — reporting failure",
-                        job.Id, prefix, outputDirLocal);
+                    _log.LogError("Job {JobId}: aerender exited 0 but no \"{Prefix}*{Ext}\" files exist in {Dir} — reporting failure",
+                        job.Id, pattern.Prefix, pattern.Extension, outputDirLocal);
                     _spooler.Enqueue("fail", job.Id, new Dictionary<string, object?>
                     {
                         ["machineId"] = machineId,