feat(p2p): implement OKX-style internal ledger escrow system

Phase 5 implementation - Internal Ledger Escrow (OKX Model):
- No blockchain transactions during P2P trades
- Blockchain tx only at deposit/withdraw
- Fast and fee-free P2P trading

Database:
- Add user_internal_balances table
- Add p2p_deposit_withdraw_requests table
- Add p2p_balance_transactions table
- Add lock_escrow_internal(), release_escrow_internal() functions
- Add process_deposit(), request_withdraw() functions

UI Components:
- Add InternalBalanceCard showing available/locked balances
- Add DepositModal for crypto deposits to P2P balance
- Add WithdrawModal for withdrawals from P2P balance
- Integrate balance card into P2PDashboard

Backend:
- Add process-withdrawal Edge Function
- Add verify-deposit Edge Function

Updated p2p-fiat.ts:
- createFiatOffer() uses internal balance lock
- confirmPaymentReceived() uses internal balance transfer
- Add internal balance management functions

web/src/components/p2p/AdList.tsx

@@ -9,7 +9,7 @@ import { TradeModal } from './TradeModal';
 import { MerchantTierBadge } from './MerchantTierBadge';
 import { getUserReputation, type P2PFiatOffer, type P2PReputation } from '@shared/lib/p2p-fiat';
 import { supabase } from '@/lib/supabase';
-import type { P2PFilters } from './OrderFilters';
+import type { P2PFilters } from './types';
 
 interface AdListProps {
   type: 'buy' | 'sell' | 'my-ads';