Add a Matter device to a second fabric using chip-tool multi-admin (open commissioning window and re-pair)

Steps

1. Commission the device onto the first fabric with chip-tool pairing ble-wifi or ble-thread, assigning a local node ID
2. From the first fabric's administrator, open an Enhanced Commissioning Window on the device: chip-tool pairing open-commissioning-window <node_id> 1 <timeout_seconds> <iteration> <discriminator>; record the printed manual pairing code
3. Switch chip-tool to the second fabric context using the --commissioner-name beta flag (or a separate storage path) so the second admin has its own fabric credentials
4. Commission the device onto the second fabric using the pairing code obtained in step 2: chip-tool --commissioner-name beta pairing code <new_node_id> <pairing_code>
5. Verify both fabrics are present on the device by reading the Operational Credentials cluster: chip-tool --commissioner-name alpha operationalcredentials nocs read 0 0
6. Remove a fabric when no longer needed with chip-tool operationalcredentials remove-fabric <fabric_index> <node_id> <endpoint>