feat(os/gapp): add unified multi-server application lifecycle

[qinyuguang]

Introduce os/gapp App to coordinate Boot, Start, Stop, and OS signal handling across multiple Server implementations, supporting graceful or forceful shutdown in one place.

• Add contrib/scheduler/gjob worker and cron servers implementing gapp.Server
• Add grpcx GrpcServerAdapter with managed non-blocking start
• Add ghttp.Server.Close for forceful shutdown; harden admin restart/shutdown
• Add gproc.StartListen for background signal handling used by gapp

Example

// main initializes and starts gRPC/HTTP servers and scheduler job servers (worker + cron).
func main() {
	ctx := gctx.GetInitCtx()

	grpcServer := grpcx.Server.New()
	controller.Register(grpcServer)

	httpServer := g.Server()
	httpServer.BindHandler("/", func(r *ghttp.Request) {
		r.Response.Write("Hello World!")
	})

	app := gapp.New(
		grpcx.NewGappServerAdapter(grpcServer),
		gapp.NewHTTPServerAdapter(httpServer),
	)
	app.Add(gjob.NewServersFromConfig(ctx, job.Handlers())...)

	app.Option(
		gapp.NewOption(func(ctx context.Context, app *gapp.App) {
			g.Log().Info(ctx, "app starting...")
		}),
	)

	if err := app.Run(ctx); err != nil {
		g.Log().Errorf(ctx, "app run failed: %+v", err)
		os.Exit(1)
	}

	g.Log().Info(ctx, "app shutdown.")
}

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