fix: add chat session summary migration

ai_knowledge_base_v2/apps/backend/alembic/versions/0005_chat_session_summary.py

@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0005_chat_session_summary"
+down_revision = "0004_daily_chat_reset_date"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("sys_chat_session", sa.Column("summary", sa.Text(), nullable=True))
+    op.add_column("sys_chat_session", sa.Column("summary_up_to_message_id", sa.BigInteger(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("sys_chat_session", "summary_up_to_message_id")
+    op.drop_column("sys_chat_session", "summary")