Add Hedera (HBAR) support for trading and funding accounts

Enable native Hedera Hashgraph (HBAR) support across funding and trading workflows. Users should be able to deposit and withdraw HBAR to/from platform funding accounts, hold HBAR in trading accounts, and trade HBAR against supported fiat and crypto pairs. Expected behavior: generate valid HBAR account IDs for deposits, display incoming deposit transactions with configurable confirmation thresholds, estimate and display network fees for withdrawals, validate external HBAR addresses on withdrawal, execute trades using HBAR balances and update user balances in real time, and display HBAR balances and transaction history in the UI. Backend requirements: connect to Hedera mainnet nodes or a reliable provider, support HBAR native token transfers, implement hot/cold custody flows with secure key management, integrate deposit/withdrawal monitoring, and surface explorer links and reconciliation data for compliance and auditing. Include rate limits, failure/error handling, and monitoring/alerting for unusual activity. Support documentation and UI labels should be updated to include HBAR.