feat(db): add Customer.add_time column + migration

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

yunke-server/migrations/versions/3892dbfab839_customer_add_time.py

@@ -0,0 +1,36 @@
+"""customer add_time
+
+Revision ID: 3892dbfab839
+Revises: 96975050fa79
+Create Date: 2026-08-05 18:37:00.679685
+
+"""
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+
+# revision identifiers, used by Alembic.
+revision: str = '3892dbfab839'
+down_revision: str | Sequence[str] | None = '96975050fa79'
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('customer', schema=None) as batch_op:
+        batch_op.add_column(sa.Column('add_time', sa.BigInteger(), nullable=True))
+
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('customer', schema=None) as batch_op:
+        batch_op.drop_column('add_time')
+
+    # ### end Alembic commands ###