W061: Update broker

Renames an existing broker. Triggered from Settings, Brokers. Same shape as W051.

Steps

1. Load the broker.

2. Check name uniqueness if changed.

3. Apply the patch. Call Customers.updateBroker.

Returns

The updated broker row.

Business rules

• Renames preserve history.

Errors

• NotFoundError. The broker was not found.
• ValidationError. Name collision.