feat(admin): link city-partner store count; fix benefitUsageRule null string

City partner storeCount jumps to /stores?partnerId=; normalize empty/null text so usage rule is not saved as literal "null.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/dukang-api/src/modules/ops/admin-stores.service.ts

@@ -17,6 +17,14 @@ import type {
   UpdateStoreStatusDto,
 } from './dto/admin-mutate.dto';
 
+/** 选填文案：空 / null / "null" 一律存库为 null，避免 String(null)==="null" */
+function normalizeStoreOptionalText(value: unknown): string | null {
+  if (value == null) return null;
+  const s = String(value).trim();
+  if (!s || /^null$/i.test(s) || /^undefined$/i.test(s)) return null;
+  return s;
+}
+
 @Injectable()
 export class AdminStoresService {
   constructor(
@@ -286,7 +294,7 @@ export class AdminStoresService {
           ...(normalizedPhone !== undefined ? { phone: normalizedPhone } : {}),
           ...(dto.intro !== undefined ? { intro: dto.intro } : {}),
           ...(dto.benefitUsageRule !== undefined
-            ? { benefitUsageRule: String(dto.benefitUsageRule).trim() || null }
+            ? { benefitUsageRule: normalizeStoreOptionalText(dto.benefitUsageRule) }
             : {}),
           ...(dto.address !== undefined ? { address: dto.address.trim() } : {}),
           ...(dto.province !== undefined ? { province: dto.province.trim() } : {}),
@@ -417,7 +425,7 @@ export class AdminStoresService {
     if (intro && (intro.length < 2 || intro.length > 500)) {
       throw new BadRequestException('门店简介须为 2~500 字');
     }
-    const benefitUsageRule = dto.benefitUsageRule?.trim() || null;
+    const benefitUsageRule = normalizeStoreOptionalText(dto.benefitUsageRule);
     if (benefitUsageRule && benefitUsageRule.length > 1000) {
       throw new BadRequestException('好客权益券使用规则最多 1000 字');
     }