fix(batch-mining): 修正grandTotalAmount重复累加问题

用户可能在多个批次中出现，之前按批次累加batchTotalAmount会导致
同一用户的收益被重复计算。改为直接累加所有用户的amount（去重）。

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

backend/services/mining-service/src/application/services/batch-mining.service.ts

@@ -273,7 +273,6 @@ export class BatchMiningService {
     }
 
     // 构建返回结果
-    let grandTotalAmount = new Decimal(0);
     const batchResults: BatchMiningPreviewResult['batches'] = [];
 
     // 计算用户总算力（用于显示）
@@ -283,6 +282,17 @@ export class BatchMiningService {
     }
     this.logger.log(`[preview] 用户总算力: ${totalUserContribution.toFixed(2)}`);
 
+    // 计算 grandTotalAmount：所有用户的收益总和（去重）
+    let grandTotalAmount = new Decimal(0);
+    const processedUsers = new Set<string>();
+    for (const [accountSequence, amount] of userAmounts) {
+      if (!processedUsers.has(accountSequence)) {
+        processedUsers.add(accountSequence);
+        grandTotalAmount = grandTotalAmount.plus(amount);
+      }
+    }
+    this.logger.log(`[preview] 计算的总金额: ${grandTotalAmount.toFixed(8)} (${processedUsers.size}个用户)`);
+
     for (const batchNum of sortedBatches) {
       const batchItems = batchGroups.get(batchNum)!;
       const batchContribution = batchContributions.get(batchNum)!;
@@ -330,8 +340,6 @@ export class BatchMiningService {
         cumulativeNetworkContribution: cumulativeContribution.toFixed(10),
         batchTotalAmount: batchTotalAmount.toFixed(8),
       });
-
-      grandTotalAmount = grandTotalAmount.plus(batchTotalAmount);
     }
 
     const result = {