feat(user): add user creation endpoint for superusers

- Add new `/userMgr/create` endpoint for superusers to create users with specified types
- Update AddUser function to accept user type parameter
- Add documentation for the new endpoint in api.md
- Remove debug log comment in auth.go

database.go

@@ -43,8 +43,8 @@ func isValidInput(input string) bool {
 	return true
 }
 
-func AddUser(username, passwd string) (int, error) { // New user registration with default type "visitor"
-	if !isValidInput(username) || !isValidInput(passwd) {
+func AddUser(username, passwd, userType string) (int, error) { // New user registration with specified type
+	if !isValidInput(username) || !isValidInput(passwd) || !isValidInput(userType) {
 		return 0, errors.New("invalid input: contains illegal characters")
 	}
 
@@ -58,7 +58,7 @@ func AddUser(username, passwd string) (int, error) { // New user registration wi
 	}
 
 	result, err := db.Exec("INSERT INTO userLogin (username, passwd, type) VALUES (?, ?, ?)",
-		username, hashedPasswd, "visitor")
+		username, hashedPasswd, userType)
 	if err != nil {
 		if strings.Contains(err.Error(), "UNIQUE constraint failed") {
 			return 0, errors.New("username already exists")