Add DOGE (Dogecoin) support for trading and funding accounts

Enable Dogecoin (DOGE) as a supported asset for both funding (deposits and withdrawals) and trading on the platform. Use case: community demand and high on-chain activity suggests adding DOGE will attract new users and increase trading volume. Expected behavior: users can deposit DOGE into their funding accounts, view DOGE balances and transaction history, place and fill orders on newly enabled DOGE trading pairs, and withdraw DOGE to external addresses. Platform responsibilities include integrating a DOGE node or third-party custodial provider, displaying DOGE market data and fees, enforcing existing KYC/AML and risk controls for DOGE activity, implementing deposit/withdrawal confirmations and minimums, and providing UI/UX elements (wallet, order entry, balances, trade history) and monitoring/alerting for DOGE network health and liquidity.