fix(push-config): 修复厂商凭据无法回显问题

- 添加 getServiceItem API，按平台精确查询推送服务配置（/services/item）
- applySelectedPlatformConfig 改用精确接口而非列表，避免 listByApp
  只返回第一条 PUSH 服务（IOS）导致 ANDROID 配置加载为空的问题

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tenant-platform/src/api/app.ts

@@ -170,6 +170,11 @@ export const appApi = {
     } as typeof res & { data: { data: FeatureService } }
   },
 
+  getServiceItem: (appKey: string, platform: string, serviceType: string) =>
+    client.get<{ data: FeatureService }>(`/apps/${appKey}/services/item`, {
+      params: { platform, serviceType },
+    }),
+
   toggleService: (appKey: string, platform: string, serviceType: string, enable: boolean) =>
     client.post<{ data: FeatureService }>(`/apps/${appKey}/services/toggle`, null, {
       params: { platform, serviceType, enable },

tenant-platform/src/views/push/PushConfigView.vue

@@ -528,17 +528,21 @@ async function loadData() {
     services.value = svcRes.data.data
     // Always default to ANDROID on load; user can switch via the platform selector
     selectedPlatform.value = 'ANDROID'
-    applySelectedPlatformConfig()
+    await applySelectedPlatformConfig()
   } finally {
     loading.value = false
   }
 }
 
-function applySelectedPlatformConfig() {
-  const raw = services.value.find(
-    s => s.serviceType === 'PUSH' && s.platform === selectedPlatform.value,
-  )?.config
-  replaceState(parseConfig(raw))
+async function applySelectedPlatformConfig() {
+  if (!app.value) return
+  try {
+    const res = await appApi.getServiceItem(app.value.appKey, selectedPlatform.value, 'PUSH')
+    replaceState(parseConfig(res.data.data?.config))
+  } catch {
+    // 该平台尚无配置，清空表单
+    replaceState(parseConfig(null))
+  }
 }
 
 function buildPayload(): PushServiceConfig {