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/runtimecfg/config.go

@@ -0,0 +1,29 @@
+package runtimecfg
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+
+	"gopkg.in/yaml.v2"
+)
+
+// Load substitutes YAML scalars from the service's separately loaded .env.
+func Load(path string, target interface{}) error {
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	var missing string
+	expanded := os.Expand(string(raw), func(key string) string {
+		value, ok := os.LookupEnv(key)
+		if !ok || value == "" {
+			missing = key
+		}
+		return strconv.Quote(value)
+	})
+	if missing != "" {
+		return fmt.Errorf("required environment variable is missing: %s", missing)
+	}
+	return yaml.Unmarshal([]byte(expanded), target)
+}