feat: 从黄果 NET hgdjnet-server 9bfbafe 导入 HKDJ 官网后端

来源：hgdjnet-server 9bfbafe10d417deea959bd53117bc88a10e60a83
项目身份 HKDJ / JHA-216，独立官网仓库，Jenkins 守卫键 hkdjnet
测试目录 /server/hkdj_net，App/Web API 30331/30332

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pub/common/utils/num.go

@@ -0,0 +1,20 @@
+package utils
+
+import (
+	"math/rand"
+	"time"
+)
+
+// CountDigits 有几位数字
+func CountDigits(i int) (count int) {
+	for i != 0 {
+		i /= 10
+		count++
+	}
+	return
+}
+
+func RandInt(min int, max int) int {
+	rand.Seed(time.Now().UnixNano())
+	return min + rand.Intn(max-min)
+}