Fix shutdown waitgroup panic (#35676)

This PR fixes a panic issue in the WaitGroup that occurs when Gitea is
shut down using Ctrl+C.
It ensures that all active connection pointers in the server are
properly tracked and forcibly closed when the hammer shutdown is
invoked.
The process remains graceful — the normal shutdown sequence runs before
the hammer is triggered, and existing connections are given a timeout
period to complete gracefully.

This PR also fixes `no logger writer` problem. Now the log close will
only be invoked when the command exit.

- Fixes #35468
- Fixes #35551
- Fixes #35559
- Replace #35578

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

main.go

@@ -44,6 +44,7 @@ func main() {
 	}
 	app := cmd.NewMainApp(cmd.AppVersion{Version: Version, Extra: formatBuiltWith()})
 	_ = cmd.RunMainApp(app, os.Args...) // all errors should have been handled by the RunMainApp
+	// flush the queued logs before exiting, it is a MUST, otherwise there will be log loss
 	log.GetManager().Close()
 }