fix(contribution): 修复系统账户查询中 nullable regionCode 的 TypeScript 类型错误

## 问题
- Prisma 生成的类型不允许在 unique where 条件中传递 null
- addContribution 方法被传入多余参数
- findByType 返回数组被当作单个对象使用

## 修复
- findByTypeAndRegion: 使用 findFirst 替代 findUnique
- ensureSystemAccountsExist: 使用 findFirst + create 替代 upsert
- addContribution: 使用 findFirst + create/update 替代 upsert
- 修正 HEADQUARTERS 账户同步事件调用参数

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

backend/services/contribution-service/src/application/services/contribution-calculation.service.ts

@@ -286,19 +286,17 @@ export class ContributionCalculationService {
         new ContributionAmount(0),
       );
       await this.systemAccountRepository.addContribution(
-        'HEADQUARTERS',
         'HEADQUARTERS',
         null,
         totalUnallocatedAmount,
       );
 
       // 发布 HEADQUARTERS 账户同步事件
-      const headquartersAccount = await this.systemAccountRepository.findByType('HEADQUARTERS');
+      const headquartersAccount = await this.systemAccountRepository.findByTypeAndRegion('HEADQUARTERS', null);
       if (headquartersAccount) {
         const hqEvent = new SystemAccountSyncedEvent(
           'HEADQUARTERS',
-          'HEADQUARTERS',  // 新增：基础类型
-          null,            // 新增：区域代码（总部没有区域）
+          null,            // 区域代码（总部没有区域）
           headquartersAccount.name,
           headquartersAccount.contributionBalance.value.toString(),
           headquartersAccount.createdAt,

backend/services/contribution-service/src/infrastructure/persistence/repositories/system-account.repository.ts

@@ -39,14 +39,16 @@ export class SystemAccountRepository {
 
   /**
    * 根据 accountType + regionCode 查找系统账户
+   * 注意：由于 regionCode 是可选字段，使用 findFirst 替代 findUnique
    */
   async findByTypeAndRegion(
     accountType: SystemAccountType,
     regionCode: string | null,
   ): Promise<SystemAccount | null> {
-    const record = await this.client.systemAccount.findUnique({
+    const record = await this.client.systemAccount.findFirst({
       where: {
-        accountType_regionCode: { accountType, regionCode },
+        accountType,
+        regionCode: regionCode === null ? { equals: null } : regionCode,
       },
     });
 
@@ -87,19 +89,25 @@ export class SystemAccountRepository {
     ];
 
     for (const account of accounts) {
-      await this.client.systemAccount.upsert({
+      // 由于 regionCode 是 nullable，使用 findFirst + create 替代 upsert
+      const existing = await this.client.systemAccount.findFirst({
         where: {
-          accountType_regionCode: { accountType: account.accountType, regionCode: null },
-        },
-        create: {
           accountType: account.accountType,
-          regionCode: null,
-          name: account.name,
-          contributionBalance: 0,
-          contributionNeverExpires: true,
+          regionCode: { equals: null },
         },
-        update: {},
       });
+
+      if (!existing) {
+        await this.client.systemAccount.create({
+          data: {
+            accountType: account.accountType,
+            regionCode: null,
+            name: account.name,
+            contributionBalance: 0,
+            contributionNeverExpires: true,
+          },
+        });
+      }
     }
   }
 
@@ -113,21 +121,32 @@ export class SystemAccountRepository {
   ): Promise<void> {
     const name = this.getAccountName(accountType, regionCode);
 
-    await this.client.systemAccount.upsert({
+    // 由于 regionCode 是 nullable，使用 findFirst + create/update 替代 upsert
+    const existing = await this.client.systemAccount.findFirst({
       where: {
-        accountType_regionCode: { accountType, regionCode },
-      },
-      create: {
         accountType,
-        regionCode,
-        name,
-        contributionBalance: amount.value,
-        contributionNeverExpires: true,
-      },
-      update: {
-        contributionBalance: { increment: amount.value },
+        regionCode: regionCode === null ? { equals: null } : regionCode,
       },
     });
+
+    if (existing) {
+      await this.client.systemAccount.update({
+        where: { id: existing.id },
+        data: {
+          contributionBalance: { increment: amount.value },
+        },
+      });
+    } else {
+      await this.client.systemAccount.create({
+        data: {
+          accountType,
+          regionCode,
+          name,
+          contributionBalance: amount.value,
+          contributionNeverExpires: true,
+        },
+      });
+    }
   }
 
   /**