feat(fc3c): migration 0013 — download_event.metadata + import_settings downloader fields

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

backend/app/models/download_event.py

@@ -2,7 +2,9 @@
 
 from datetime import datetime
 
+import sqlalchemy as sa
 from sqlalchemy import BigInteger, DateTime, ForeignKey, Integer, String, Text, func
+from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import Mapped, mapped_column
 
 from .base import Base
@@ -18,7 +20,7 @@ class DownloadEvent(Base):
     post_id: Mapped[int | None] = mapped_column(
         ForeignKey("post.id", ondelete="SET NULL"), nullable=True, index=True
     )
-    status: Mapped[str] = mapped_column(String(32), nullable=False)  # pending|running|ok|error
+    status: Mapped[str] = mapped_column(String(32), nullable=False)  # pending|running|ok|error|skipped
     started_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, server_default=func.now()
     )
@@ -26,3 +28,7 @@ class DownloadEvent(Base):
     bytes_downloaded: Mapped[int] = mapped_column(BigInteger, nullable=False, default=0)
     files_count: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
     error: Mapped[str | None] = mapped_column(Text, nullable=True)
+    metadata_: Mapped[dict] = mapped_column(
+        "metadata", JSONB, nullable=False, default=dict,
+        server_default=sa.text("'{}'::jsonb"),
+    )