feat: add alembic migration script to merge multiple heads for deployment

backend/alembic/versions/h1a2b3c4d5e6_merge_multiple_heads.py

@@ -0,0 +1,27 @@
+"""merge alembic heads for deployment
+
+Revision ID: h1a2b3c4d5e6
+Revises: c3d4e5f6a7b8, f1a2b3c4d5e6, g1b2c3d4e5f6
+Create Date: 2026-04-30 12:00:00.000000
+"""
+
+from typing import Sequence, Union
+
+
+# revision identifiers, used by Alembic.
+revision: str = "h1a2b3c4d5e6"
+down_revision: Union[str, Sequence[str], None] = (
+    "c3d4e5f6a7b8",
+    "f1a2b3c4d5e6",
+    "g1b2c3d4e5f6",
+)
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    pass
+
+
+def downgrade() -> None:
+    pass