fix(payment): 修复后端返回空supported_types时支付提供商卡片消失的问题

统一处理后端返回的null类型supported_types，将其标准化为空数组，避免调用includes()时报错导致卡片无法显示，同时修复多处相关的类型判断逻辑

frontend/src/components/payment/PaymentProviderDialog.vue

@@ -658,7 +658,9 @@ function reset(defaultKey: string) {
 function loadProvider(provider: ProviderInstance) {
   form.name = provider.name
   form.provider_key = provider.provider_key
-  form.supported_types = provider.supported_types
+  form.supported_types = Array.isArray(provider.supported_types)
+    ? [...provider.supported_types]
+    : []
   form.enabled = provider.enabled
   // Coerce to a valid value for this provider. Guards against stale data
   // (e.g. "popup" written by an older client) showing up as an unselected

frontend/src/components/payment/ProviderCard.vue

@@ -104,6 +104,6 @@ const modeLabel = computed(() => {
 })
 
 function isSelected(type: string): boolean {
-  return props.provider.supported_types.includes(type)
+  return Array.isArray(props.provider.supported_types) && props.provider.supported_types.includes(type)
 }
 </script>