Proposal #48: Lower Direct Participation Threshold to 10%

During the Kimi-K2.6 bootstrap, the 30% direct participation threshold proved hard to meet. To avoid the risk of Kimi-K2.6 becoming ineligible in a future epoch and to simplify onboarding of further models, this proposal lowers the threshold to 10%. The security model is preserved: PoC validation itself is unchanged and still requires a supermajority of validation power to accept results. It is expedited so the change takes effect before the next PoC.