Remove: FeeRouter CL8Y LP/burn/podium/Rabbit split; replace with Arena DOUB routing

Context

Replace legacy FeeRouter five-sink CL8Y model with TimeArena DOUB routing. Parent epic: #238 (closed).

Relevant files

• contracts/src/FeeRouter.sol
• Sinks: DoubLPIncentives.sol, EcosystemTreasury.sol, CL8YProtocolTreasury.sol, PodiumPool.sol
• docs/onchain/fee-routing-and-governance.md
• frontend/src/pages/TimeCurveProtocolPage.tsx (fee-sink footer)

Acceptance criteria

• v2 buy path routes DOUB per spec (40% live pools + 30% seed + 30% admin vault) without legacy 30/40/20/0/10 CL8Y table
• PodiumPool redesigned or replaced with per-podium DOUB vaults (4× current + 4× seed + 1× admin)

Verification checklist

• Forge test: buy N DOUB → measured vault balances match bps
• No CL8Y burn sink in v2 buy path