Rescue Paperjet v1 implementation

backend/app/models/annotation_state.py

@@ -1,15 +1,19 @@
 """AnnotationState model — current working annotation layer per document."""
 
-from datetime import datetime, timezone
+from datetime import UTC, datetime
+from typing import TYPE_CHECKING
 
 from sqlalchemy import ForeignKey, Text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.db import Base
 
+if TYPE_CHECKING:
+    from app.models.document import Document
+
 
 def _now_iso() -> str:
-    return datetime.now(timezone.utc).isoformat()
+    return datetime.now(UTC).isoformat()
 
 
 class AnnotationState(Base):