fix: alembic migration uses table name mps_page_session, not class name

op.add_column takes the actual SQLite table name, not the SQLAlchemy
model class name. PageSession maps to mps_page_session via CLASS_TO_TABLE.

make_post_sell/scripts/alembic/versions/b3f7a2c8d1e5_add_is_owner_to_page_session.py

@@ -17,10 +17,10 @@ depends_on = None
 
 def upgrade():
     op.add_column(
-        "PageSession",
+        "mps_page_session",
         sa.Column("is_owner", sa.Boolean(), nullable=True),
     )
 
 
 def downgrade():
-    op.drop_column("PageSession", "is_owner")
+    op.drop_column("mps_page_session", "is_owner")