fix: 修复账号修改代理更新无效的bug

frontend/src/components/account/BulkEditAccountModal.vue

@@ -831,7 +831,8 @@ const buildUpdatePayload = (): Record<string, unknown> | null => {
   let credentialsChanged = false
 
   if (enableProxy.value) {
-    updates.proxy_id = proxyId.value
+    // 后端期望 proxy_id: 0 表示清除代理，而不是 null
+    updates.proxy_id = proxyId.value === null ? 0 : proxyId.value
   }
 
   if (enableConcurrency.value) {

frontend/src/components/account/EditAccountModal.vue

@@ -1053,6 +1053,10 @@ const handleSubmit = async () => {
   submitting.value = true
   try {
     const updatePayload: Record<string, unknown> = { ...form }
+    // 后端期望 proxy_id: 0 表示清除代理，而不是 null
+    if (updatePayload.proxy_id === null) {
+      updatePayload.proxy_id = 0
+    }
 
     // For apikey type, handle credentials update
     if (props.account.type === 'apikey') {