Self-hosted dashboard and admin auth (#4837)

Co-authored-by: kartik-mem0 <kartik.labhshetwar@mem0.ai>

server/alembic/versions/004_unique_admin_role.py

@@ -0,0 +1,31 @@
+"""Enforce at-most-one admin via partial unique index
+
+Revision ID: 004
+Revises: 003
+Create Date: 2026-04-21
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "004"
+down_revision: Union[str, None] = "003"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_index(
+        "ix_users_only_one_admin",
+        "users",
+        ["role"],
+        unique=True,
+        postgresql_where=sa.text("role = 'admin'"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_users_only_one_admin", table_name="users")