feat(push-gateway): 修复WebSocket并发写竞争并添加DEV_MODE鉴权

hub.go 重写用send chan+单写协程模式避免并发写竞争

handler.go 加DEV_MODE dev-token支持+broadcast端点

config.go 加DevMode/RedisURL字段

services/push-gateway/internal/config/config.go

@@ -2,18 +2,25 @@ package config
 
 import "os"
 
+// Config 持有 push-gateway 运行时配置
 type Config struct {
 	Port      string
 	JWTSecret string
+	DevMode   bool
+	RedisURL  string
 }
 
+// Load 从环境变量加载配置并提供默认值
 func Load() *Config {
 	return &Config{
 		Port:      getEnv("PUSH_GATEWAY_PORT", "8081"),
 		JWTSecret: getEnv("JWT_SECRET", "p1-dev-secret-change-in-production"),
+		DevMode:   getEnv("DEV_MODE", "false") == "true",
+		RedisURL:  getEnv("REDIS_URL", ""),
 	}
 }
 
+// getEnv 读取环境变量，缺失时返回 fallback
 func getEnv(key, fallback string) string {
 	if v := os.Getenv(key); v != "" {
 		return v