feat: prepare RAG evidence and compatible chat requests

backend/app/models/rag.py

@@ -0,0 +1,18 @@
+from datetime import datetime
+
+from sqlalchemy import JSON, DateTime, ForeignKey, String, func
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.session import Base
+
+
+class RagContext(Base):
+    __tablename__ = "rag_contexts"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True)
+    retrieval_run_id: Mapped[str] = mapped_column(ForeignKey("retrieval_runs.id"), index=True)
+    created_by: Mapped[int] = mapped_column(ForeignKey("users.id"))
+    response: Mapped[dict] = mapped_column(JSON, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), index=True
+    )