feat(cmd): add -R auto-reload flag for periodic config refresh

Introduce -R <duration> flag (e.g., -R 30s, -R 1m) that triggers
periodic config reload. Combined with -C URL support, this enables
centralized fleet management where nodes poll a remote config server.

The reload goroutine reuses the existing SIGHUP reloadConfig path:
parser.Parse() → loader.Load() → p.run(cfg). When -R is zero
(default) behavior is unchanged; SIGHUP still works independently.

cmd/gost/main.go

@@ -11,6 +11,7 @@ import (
 	"runtime"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/go-gost/core/logger"
 	xlogger "github.com/go-gost/x/logger"
@@ -36,6 +37,7 @@ var (
 	trace        bool
 	apiAddr      string
 	metricsAddr  string
+	reload       time.Duration
 )
 
 func init() {
@@ -87,13 +89,14 @@ func init() {
 
 	flag.Var(&services, "L", "service list")
 	flag.Var(&nodes, "F", "chain node list")
-	flag.Var(&cfgFiles, "C", "configuration file(s)")
+	flag.Var(&cfgFiles, "C", "config file(s), URL(s), or inline JSON")
 	flag.BoolVar(&printVersion, "V", false, "print version")
 	flag.StringVar(&outputFormat, "O", "", "output format, one of yaml|json format")
 	flag.BoolVar(&debug, "D", false, "debug mode")
 	flag.BoolVar(&trace, "DD", false, "trace mode")
 	flag.StringVar(&apiAddr, "api", "", "api service address")
 	flag.StringVar(&metricsAddr, "metrics", "", "metrics service address")
+	flag.DurationVar(&reload, "R", 0, "auto reload period (e.g. 30s, 1m)")
 	flag.Parse()
 
 	if printVersion {

cmd/gost/program.go

@@ -8,6 +8,7 @@ import (
 	"os/signal"
 	"strings"
 	"syscall"
+	"time"
 
 	"github.com/go-gost/core/auth"
 	"github.com/go-gost/core/logger"
@@ -193,6 +194,13 @@ func (p *program) reload(ctx context.Context) {
 	c := make(chan os.Signal, 1)
 	signal.Notify(c, syscall.SIGHUP)
 
+	var ticker <-chan time.Time
+	if reload > 0 {
+		t := time.NewTicker(reload)
+		defer t.Stop()
+		ticker = t.C
+	}
+
 	for {
 		select {
 		case <-c:
@@ -202,6 +210,13 @@ func (p *program) reload(ctx context.Context) {
 				logger.Default().Info("config reloaded")
 			}
 
+		case <-ticker:
+			if err := p.reloadConfig(); err != nil {
+				logger.Default().Errorf("auto reload: %v", err)
+			} else {
+				logger.Default().Debug("config auto reloaded")
+			}
+
 		case <-ctx.Done():
 			return
 		}