Fix Alembic 0003 duplicate role_enum constraint failure

[chrystianmartins]

Motivation

• The migration 0003_update_user_role_enum_for_new_auth_flow was failing during alembic upgrade with psycopg.errors.DuplicateObject because the role_enum check constraint was being created twice (manually via raw SQL and implicitly via the enum type alteration).

Description

• Removed the manual ALTER TABLE ... ADD CONSTRAINT role_enum statements from pool-coordinator/alembic/versions/0003_update_user_role_enum_for_new_auth_flow.py and retained the DROP CONSTRAINT IF EXISTS cleanup, relying on op.batch_alter_table(...).alter_column(..., type_=sa.Enum(..., create_constraint=True)) to recreate the constraint exactly once.

Testing

• Ran make test which passed: pool-coordinator tests 39 passed, 3 skipped; pool-gateway tests 8 passed; and worker unit/cli tests passed.

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Codex Task