Prop 36: TX Chain Upgrade v6.1.0

# TX Chain Upgrade v6.1.0 includes:

1. Chain Registry fix

At the moment TX is still displayed as CORE in Keplr. This upgrade will fix that and allow us to merge a rebrand PR into the Chain Registry.
Technical details: It updates the DenomUnits display from core to tx so the chain passes Chain Registry validation and can be listed. Metadata only — no impact on balances or chain operations.

2. PSE distribution fix

While testing the latest binary on testnet we found an issue with division by zero. Mainnet is not affected at the moment, but this upgrade is required before PSE starts.
Technical details: It fixes a division-by-zero in PSE distributions when a delegator has a score but zero delegation balance (e.g. after validator slashing).

We have submitted this as an expedited proposal so that the rebrand of COREUM to TX can be finalized in a timely manner.