Removes the mobile-device binding on a series. After unlocking, any authenticated caller (web, API key, or mobile) can emit invoices on the series again.
The mobile device that owns the lock can always unlock.
A different mobile device needs force: true in the body and firm-admin rights to override.
Legacy API-key callers bypass the device check and can force-unlock unconditionally (intended for admin tooling).
Returns the updated series object. is_locked is false and lock is null.
Any offline reservations the previous device had not yet synced are still valid: the lock only gates new invoice creation. If a locked device has queued invoices in its outbox, coordinate with the user before force-unlocking — their next sync will still succeed if their reservation tokens are still pending on the server.