fix: source_channel enum에 'news' 추가 (ORM 누락)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/models/document.py

@@ -70,7 +70,7 @@ class Document(Base):
     # 메타데이터
     source_channel: Mapped[str | None] = mapped_column(
         Enum("law_monitor", "devonagent", "email", "web_clip",
-             "tksafety", "inbox_route", "manual", "drive_sync",
+             "tksafety", "inbox_route", "manual", "drive_sync", "news",
              name="source_channel")
     )
     data_origin: Mapped[str | None] = mapped_column(