feat: govern file lifecycle and connector writes

src/govoplan_files/backend/db/models.py

@@ -214,6 +214,16 @@ class FileAsset(Base, TimestampMixin):
     deleted_at: Mapped[datetime | None] = mapped_column(
         DateTime(timezone=True), nullable=True, index=True
     )
+    retained_until: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True, index=True
+    )
+    legal_hold: Mapped[bool] = mapped_column(
+        Boolean, default=False, nullable=False, index=True
+    )
+    lifecycle_revision: Mapped[int] = mapped_column(
+        Integer, default=1, nullable=False
+    )
+    lifecycle_reason: Mapped[str | None] = mapped_column(String(500), nullable=True)
     metadata_: Mapped[dict[str, Any] | None] = mapped_column(
         "metadata", JSON, nullable=True
     )