feat: Go 重写后端，替换 Python FastAPI

用 Go (Gin + GORM + SQLite) 重写整个后端：
- 单二进制部署，不依赖 Python/pip/SDK
- net/http 原生客户端，无 Cloudflare TLS 指纹问题
- 多阶段 Dockerfile：Node 构建前端 + Go 构建后端 + Alpine 运行
- 内存占用从 ~95MB 降至 ~3MB
- 完整保留所有 API 路由、JWT 认证、API Key 权限、审计日志

handlers/settings.go

@@ -0,0 +1,70 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"airwallex-admin/models"
+	"airwallex-admin/services"
+)
+
+var sensitiveKeys = map[string]bool{
+	"airwallex_api_key":  true,
+	"proxy_password":     true,
+	"admin_password_hash": true,
+}
+
+func GetSettings(c *gin.Context) {
+	var settings []models.SystemSetting
+	models.DB.Find(&settings)
+
+	for i, s := range settings {
+		if sensitiveKeys[s.Key] {
+			settings[i].Value = "********"
+		}
+	}
+
+	c.JSON(http.StatusOK, settings)
+}
+
+type settingItem struct {
+	Key   string `json:"key"`
+	Value string `json:"value"`
+}
+
+func UpdateSettings(c *gin.Context) {
+	var items []settingItem
+	if err := c.ShouldBindJSON(&items); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": "Invalid request body"})
+		return
+	}
+
+	for _, item := range items {
+		if item.Value == "********" {
+			continue
+		}
+		encrypted := sensitiveKeys[item.Key]
+		models.SetSetting(models.DB, item.Key, item.Value, encrypted)
+	}
+
+	username := c.GetString("username")
+	models.DB.Create(&models.AuditLog{
+		Action:       "update_settings",
+		ResourceType: "settings",
+		Operator:     username,
+		IPAddress:    c.ClientIP(),
+	})
+
+	c.JSON(http.StatusOK, gin.H{"detail": "Settings updated"})
+}
+
+func TestConnection(c *gin.Context) {
+	result := services.TestConnection(models.DB)
+	c.JSON(http.StatusOK, result)
+}
+
+func TestProxy(c *gin.Context) {
+	result := services.TestProxy(models.DB)
+	c.JSON(http.StatusOK, result)
+}