Plan migration from local data.db to cloud-backed storage

Context

Future work from docs/superpowers/specs/2026-05-24-local-libsql-migration-design.md.

The local libsql migration and Turso cloud configuration model are prerequisites. This issue should define an upgrade-friendly path for existing agents that already have local data.db state.

Scope

• Define how existing local data.db contents move to a cloud-backed primary or replica setup.
• Preserve upgrade-friendly behavior for already-deployed agents.
• Avoid sandbox deletion, agent recreation, or manual state surgery.
• Define dry-run, validation, rollback, and observability requirements.

Acceptance Criteria

• Migration path works for already-deployed agents with existing data.
• The process validates schema version and data integrity before switching modes.
• Failures leave the agent in a usable local-only state.
• Documentation states operator steps and recovery behavior.

Out Of Scope

• Initial local libsql driver migration.
• General cloud backup UX.
• Dashboard visualizations for sync state.

Start by reading docs/superpowers/specs/2026-05-24-local-libsql-migration-design.md and the existing local data.db and Turso configuration behavior it describes. Define the upgrade, validation, dry-run, rollback, and observability requirements for deployed agents. Done means the migration preserves existing state, validates schema and integrity, and leaves failures usable in local-only mode with documented operator recovery steps.