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

services/audit.go

@@ -0,0 +1,34 @@
+package services
+
+import (
+	"airwallex-admin/models"
+
+	"gorm.io/gorm"
+)
+
+// CreateAuditLog creates a new audit log entry.
+func CreateAuditLog(db *gorm.DB, action, resourceType, operator, resourceID, ipAddress, details string) {
+	log := models.AuditLog{
+		Action:       action,
+		ResourceType: resourceType,
+		ResourceID:   resourceID,
+		Operator:     operator,
+		IPAddress:    ipAddress,
+		Details:      details,
+	}
+	db.Create(&log)
+}
+
+// CreateCardLog creates a new card operation log entry.
+func CreateCardLog(db *gorm.DB, action, status, operator, cardID, cardholderID, requestData, responseData string) {
+	log := models.CardLog{
+		CardID:       cardID,
+		CardholderID: cardholderID,
+		Action:       action,
+		Status:       status,
+		Operator:     operator,
+		RequestData:  requestData,
+		ResponseData: responseData,
+	}
+	db.Create(&log)
+}