- revision="0003", down_revision="0002"
- upgrade(): collects null-user object_keys, deletes document_topics cascade,
deletes null-user documents, removes MinIO objects (skip if MINIO_ENDPOINT unset),
deletes all topics (D-10), alters documents.user_id NOT NULL via batch_alter_table,
creates ix_topics_user_id index, reconciles quotas.used_bytes from SUM(size_bytes)
- downgrade(): drops ix_topics_user_id, reverts user_id to nullable; documents not restored
- batch_alter_table ensures SQLite compatibility for test suite
- MinIO step gated on MINIO_ENDPOINT env var for safe SQLite test runs
curo1305