fix: support labeled action for pull_request events in track_progress (#1586)

Adds "labeled" to the valid pull_request actions for track_progress,
mirroring the existing support for issue events. Previously, adding
a label to a PR (e.g. to trigger a label-driven Claude review) would
fail validation even though the same pattern works for issues.

Fixes #1585

src/modes/detector.ts

@@ -103,6 +103,7 @@ function validateTrackProgressEvent(context: GitHubContext): void {
       "synchronize",
       "ready_for_review",
       "reopened",
+      "labeled",
     ];
     if (!validActions.includes(context.eventAction)) {
       throw new Error(