fix(scripts): marker reprocess SQL — CAST(:payload AS jsonb) 로 named-param 충돌 해소

`:payload::jsonb` 의 `::` postfix 캐스트가 SQLAlchemy text() 의 named-param prefix
`:` 와 충돌해 asyncpg syntax error. doc 3757 sample reprocess 시 발견.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/marker_reprocess_existing_success.py

@@ -126,9 +126,11 @@ async def run(*, apply: bool, only_ids: set[int] | None, snapshot_csv: str | Non
 
             # enqueue — UNIQUE(document_id, stage) WHERE status IN ('pending', 'processing')
             # 가 있으므로 활성 markdown 행이 없는 doc 만 통과. 충돌 시 silent skip.
+            # CAST(:payload AS jsonb) — `::jsonb` postfix 캐스트는 SQLAlchemy text()
+            # 의 named-param prefix `:` 와 충돌해 syntax error 발생.
             ENQUEUE_SQL = text("""
                 INSERT INTO processing_queue (document_id, stage, status, payload)
-                VALUES (:doc_id, 'markdown', 'pending', :payload::jsonb)
+                VALUES (:doc_id, 'markdown', 'pending', CAST(:payload AS jsonb))
                 ON CONFLICT DO NOTHING
             """)