fix(news): backfill INTERVAL bind 을 make_interval(days=>:days) 로 교체

asyncpg 가 :days || ' days' 의 int → text 암묵 변환을 거부함.
make_interval 사용으로 int 그대로 바인딩 가능.

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

scripts/news_chunk_country_backfill.py

@@ -48,7 +48,7 @@ FROM documents
 WHERE source_channel = 'news'
   AND deleted_at IS NULL
   AND extracted_text IS NOT NULL
-  AND created_at >= NOW() - (:days || ' days')::INTERVAL
+  AND created_at >= NOW() - make_interval(days => :days)
 """
 
 SAMPLE_SQL = """
@@ -59,7 +59,7 @@ FROM documents d
 WHERE d.source_channel = 'news'
   AND d.deleted_at IS NULL
   AND d.extracted_text IS NOT NULL
-  AND d.created_at >= NOW() - (:days || ' days')::INTERVAL
+  AND d.created_at >= NOW() - make_interval(days => :days)
 ORDER BY d.created_at ASC
 LIMIT 5
 """
@@ -70,7 +70,7 @@ FROM documents d
 WHERE d.source_channel = 'news'
   AND d.deleted_at IS NULL
   AND d.extracted_text IS NOT NULL
-  AND d.created_at >= NOW() - (:days || ' days')::INTERVAL
+  AND d.created_at >= NOW() - make_interval(days => :days)
 ORDER BY d.created_at ASC
 """