refactor: align backend with company-site-member schema and system-level RBAC groups

app/models/permission_group_member.py

@@ -0,0 +1,20 @@
+from datetime import datetime
+from uuid import uuid4
+
+from sqlalchemy import DateTime, ForeignKey, String, UniqueConstraint, func
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.db.base import Base
+
+
+class PermissionGroupMember(Base):
+    __tablename__ = "permission_group_members"
+    __table_args__ = (UniqueConstraint("group_id", "authentik_sub", name="uq_permission_group_members_group_sub"),)
+
+    id: Mapped[str] = mapped_column(UUID(as_uuid=False), primary_key=True, default=lambda: str(uuid4()))
+    group_id: Mapped[str] = mapped_column(
+        UUID(as_uuid=False), ForeignKey("permission_groups.id", ondelete="CASCADE"), nullable=False
+    )
+    authentik_sub: Mapped[str] = mapped_column(String(255), nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now(), nullable=False)