fix(blockchain): use amountFormatted to rebuild TokenAmount from DB

Previously used amount (raw) with hardcoded 18 decimals, which caused
incorrect formatting for USDT (6 decimals). Now uses amountFormatted
which is already correctly formatted during deposit detection.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/blockchain-service/src/infrastructure/persistence/mappers/deposit-transaction.mapper.ts

@@ -17,6 +17,11 @@ export class DepositTransactionMapper {
       throw new Error(`DepositTransaction ${prisma.id} missing accountSequence or userId`);
     }
 
+    // 使用 amountFormatted 重建 TokenAmount
+    // amountFormatted 已经是正确的人类可读格式（如 1000000.00000000）
+    // 用 decimals=8 与 toFixed(8) 保持一致，确保 toFixed(8) 返回相同的值
+    const amount = TokenAmount.fromFormatted(prisma.amountFormatted.toString(), 8);
+
     const props: DepositTransactionProps = {
       id: prisma.id,
       chainType: ChainType.create(prisma.chainType),
@@ -24,7 +29,7 @@ export class DepositTransactionMapper {
       fromAddress: EvmAddress.fromUnchecked(prisma.fromAddress),
       toAddress: EvmAddress.fromUnchecked(prisma.toAddress),
       tokenContract: EvmAddress.fromUnchecked(prisma.tokenContract),
-      amount: TokenAmount.fromDecimal(prisma.amount, 18),
+      amount,
       blockNumber: BlockNumber.create(prisma.blockNumber),
       blockTimestamp: prisma.blockTimestamp,
       logIndex: prisma.logIndex,