- Add schema v16 migration that creates workflow_steps and backfills rows from legacy config.workflowSteps data
- Update legacy file-to-SQLite migration to insert workflow step definitions into workflow_steps while preserving nextWorkflowStepId
- Refactor TaskStore workflow step create/list/get/update/delete paths to read and write workflow_steps instead of config JSON
- Adjust db migration tests and AGENTS.md storage docs to reflect the new workflow_steps table model