feat: establish core backend API server with S2A proxy, configuration, and mail services, alongside frontend email configuration page and toast component.

frontend/src/components/common/Toast.tsx

@@ -78,7 +78,7 @@ function ToastContainer({ toasts, onRemove }: ToastContainerProps) {
     if (toasts.length === 0) return null
 
     return (
-        <div className="fixed bottom-6 right-6 z-[9999] space-y-3">
+        <div className="fixed top-6 right-6 z-[9999] space-y-3">
             {toasts.map((toast) => (
                 <ToastItem key={toast.id} toast={toast} onRemove={onRemove} />
             ))}

frontend/src/pages/EmailConfig.tsx

@@ -1,13 +1,15 @@
 import { useState, useEffect } from 'react'
 import { CheckCircle, Save, Mail, Plus, Trash2, TestTube, Loader2, Settings, Server } from 'lucide-react'
-import { Card, CardHeader, CardTitle, CardContent, Button, Input } from '../components/common'
+import { Card, CardHeader, CardTitle, CardContent, Button, Input, useToast } from '../components/common'
 import { useConfig } from '../hooks/useConfig'
 import type { MailServiceConfig } from '../types'
 
 export default function EmailConfig() {
     const { config, updateEmailConfig } = useConfig()
+    const toast = useToast()
 
     const [saved, setSaved] = useState(false)
+    const [saving, setSaving] = useState(false)
     const [services, setServices] = useState<MailServiceConfig[]>(config.email?.services || [])
     const [testingIndex, setTestingIndex] = useState<number | null>(null)
     const [testResults, setTestResults] = useState<Record<number, { success: boolean; message: string }>>({})
@@ -20,6 +22,12 @@ export default function EmailConfig() {
     }, [config.email?.services])
 
     const handleSave = async () => {
+        if (services.length === 0) {
+            toast.warning('请至少添加一个邮箱服务')
+            return
+        }
+
+        setSaving(true)
         // 保存到前端 context
         updateEmailConfig({ services })
 
@@ -31,13 +39,20 @@ export default function EmailConfig() {
                 body: JSON.stringify({ services }),
             })
 
-            if (res.ok) {
+            const data = await res.json()
+
+            if (res.ok && data.code === 0) {
                 setSaved(true)
                 setTimeout(() => setSaved(false), 2000)
+                toast.success(`保存成功: ${data.data.message}`)
+            } else {
+                toast.error('保存失败: ' + (data.message || '未知错误'))
             }
         } catch (error) {
             console.error('保存失败:', error)
+            toast.error('保存失败: ' + (error instanceof Error ? error.message : '网络错误'))
         }
+        setSaving(false)
     }
 
     const handleAddService = () => {
@@ -121,9 +136,11 @@ export default function EmailConfig() {
                     </Button>
                     <Button
                         onClick={handleSave}
+                        disabled={saving}
+                        loading={saving}
                         icon={saved ? <CheckCircle className="h-4 w-4" /> : <Save className="h-4 w-4" />}
                     >
-                        {saved ? '已保存' : '保存配置'}
+                        {saved ? '已保存' : saving ? '保存中...' : '保存配置'}
                     </Button>
                 </div>
             </div>