argparse with --dry-run, async orchestrator that loops the 4 business
tables, and three step stubs (Step 1: users -> workspace creation;
Step 2: UPDATE tables from users.default_workspace_id; Step 3: orphan
rows -> legacy_workspace anchor at the LOCK'd nil UUID). Step bodies
are filled in T5.5-T5.7 alongside their tests.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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