feat: implement system configuration page with core settings for S2A, pooling, and proxy.

frontend/src/pages/Config.tsx

@@ -35,7 +35,7 @@ export default function Config() {
     try {
       const res = await fetch('/api/config')
       const data = await res.json()
-      if (data.success) {
+      if (data.code === 0 && data.data) {
         setEditS2ABase(data.data.s2a_api_base || '')
         setEditS2AKey(data.data.s2a_admin_key || '')
         setEditConcurrency(data.data.concurrency || 2)
@@ -80,11 +80,11 @@ export default function Config() {
         }),
       })
       const data = await res.json()
-      if (data.success) {
+      if (data.code === 0) {
         setMessage({ type: 'success', text: '配置已保存' })
         fetchServerConfig()
       } else {
-        setMessage({ type: 'error', text: data.error || '保存失败' })
+        setMessage({ type: 'error', text: data.message || '保存失败' })
       }
     } catch (error) {
       setMessage({ type: 'error', text: '网络错误' })