feat(idp): add keycloak-first support with authentik fallback

backend/app/models/user.py

@@ -1,7 +1,7 @@
 from datetime import datetime
 from uuid import uuid4
 
-from sqlalchemy import Boolean, DateTime, Integer, String, func
+from sqlalchemy import Boolean, DateTime, String, func
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column
 
@@ -13,7 +13,7 @@ class User(Base):
 
     id: Mapped[str] = mapped_column(UUID(as_uuid=False), primary_key=True, default=lambda: str(uuid4()))
     user_sub: Mapped[str] = mapped_column(String(255), unique=True, nullable=False, index=True)
-    idp_user_id: Mapped[int | None] = mapped_column(Integer)
+    idp_user_id: Mapped[str | None] = mapped_column(String(128))
     username: Mapped[str | None] = mapped_column(String(255), unique=True)
     email: Mapped[str | None] = mapped_column(String(320))
     display_name: Mapped[str | None] = mapped_column(String(255))