fix: mark assets rejected when faces API confidence is below threshold

Previously, assets that passed embedding-phase selection but failed the
faces API confidence check in execute_jobs were silently skipped with no
tracker entry. They appeared as valid candidates on every future run,
were re-selected, and re-skipped in an endless cycle. Now they are
marked rejected so they are excluded from future runs. RETRY_REJECTED=true
clears them if Immich later re-processes the image.

winnow/executor.py

@@ -231,6 +231,7 @@ def execute_jobs(jobs: list[dict]) -> None:
                                 f"[yellow]Skipped {asset['id']}"
                                 f" (detection confidence {conf:.2f} < {Config.MIN_CONFIDENCE})[/yellow]"
                             )
+                            mark_rejected(asset["id"], person_name=name)
                             progress.advance(job_task)
                             progress.advance(overall_task)
                             continue