feat(auth): add oauth_identities table for Google/Microsoft sign-in

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/alembic/versions/b1fad5ddf357_add_oauth_identities.py

@@ -0,0 +1,39 @@
+"""add oauth_identities
+
+Revision ID: b1fad5ddf357
+Revises: c0f3a4b7e91d
+Create Date: 2026-05-06 07:17:11.374555
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'b1fad5ddf357'
+down_revision: Union[str, None] = 'c0f3a4b7e91d'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "oauth_identities",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True),
+        sa.Column("user_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("provider", sa.String(20), nullable=False),
+        sa.Column("provider_subject", sa.String(255), nullable=False),
+        sa.Column("provider_email_at_link", sa.String(255), nullable=False),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.UniqueConstraint("provider", "provider_subject", name="uq_oauth_identities_provider_subject"),
+    )
+    op.create_index("ix_oauth_identities_user_id", "oauth_identities", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_oauth_identities_user_id", table_name="oauth_identities")
+    op.drop_table("oauth_identities")