On-chain configurability for affiliate/referrer fees

[ibruno]

Currently, affiliate/referrer fees are defined off-chain within the signed Order object (fields like feeRateBps, referrer, affiliate, affiliatePercentage). The contract only enforces validation and distribution at fill time, respecting the global MAX_FEE_RATE_BIPS.

This design provides flexibility but limits transparency: the wallet that receives fees cannot adjust rates on-chain, and users must rely on new signed orders to reflect different conditions.

Idea:
Introduce optional on-chain configurability for these parameters (similar to how the admin controls forkastFeeReceiver and forkastBaseFeeRate). This would allow forks to:

• Register their fee splits publicly, with events for visibility
• Prevent silent changes off-chain
• Increase trust in white-label forks and their governance