Add schema-versioning/migration tooling for the local stores

[JSONbored]

Problem: No migration tooling exists for the miner's local stores, unlike the main repo's migrations/ discipline — this is the packaging-facing half of the schema-versioning robustness item above.

Area: AMS / Self-host

Proposal: Build a small migration-runner CLI command that applies pending schema changes to an operator's existing local database files.

Deliverables:

• A working migrate command for the miner's local stores.

Boundaries:

• Depends on "Add schema versioning to the local SQLite stores" above for the underlying version-tracking mechanism.

[linear-code]

JSO-3531