feat: accumulate and withdraw fees

[Sikkra]

Implements Bounty 2C from #2: Withdraw Function.

Changes:

• Keeps collected fees in IntuitionFeeProxy instead of forwarding them immediately.
• Adds withdrawFees(address payable recipient, uint256 amount) for whitelisted admins or the current fee recipient.
• Rejects unauthorized callers, zero recipients, over-balance withdrawals, and failed transfers.
• Emits FeesWithdrawn for successful withdrawals.
• Updates fee collection tests to assert accumulated proxy balance and adds withdrawal edge-case coverage.

Verification:

• npm run compile
• npm test (38 passing)

Payout address (Base): 0xa925FdD65a0f34bb415Bae1c57536Be33AbCfA92