refactor: migrate backend main function

backend/cli/cli.go

@@ -13,6 +13,10 @@ type CLIArgs struct {
 	Config string
 	// Init indicates whether to initialize the calendar system before running.
 	Init bool
+	// Username is the first admin user's name; required together with --init.
+	Username string
+	// Password is the first admin user's password; required together with --init.
+	Password string
 }
 
 // Parse parses the command-line arguments via the standard flag package and
@@ -31,8 +35,12 @@ func Parse() *CLIArgs {
 	}
 
 	// --config maps to the legacy -c/--config (required), --init to -i/--init.
+	// --username/--password replace the legacy interactive GetUsernamePassword
+	// prompt and are required together with --init.
 	flag.StringVar(&args.Config, "config", "", "The configuration file `CONFIG_TOML` for coconut-leaf")
 	flag.BoolVar(&args.Init, "init", false, "Set for initialize the calendar system")
+	flag.StringVar(&args.Username, "username", "", "The first admin user's name (required with --init)")
+	flag.StringVar(&args.Password, "password", "", "The first admin user's password (required with --init)")
 
 	flag.Parse()