feat(userMgr): add user removal functionality

- Implement RemoveUser function in database.go to delete users
- Add RemoveUserHandler to handle HTTP requests for user removal
- Update API documentation with new /userMgr/remove endpoint
- Add route for user removal in router.go

database.go

@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"strconv"
 	"strings"
 	"time"
 
@@ -84,6 +85,28 @@ func AddUser(username, passwd, userType string) (int, error) { // New user regis
 	return int(lastID), nil
 }
 
+func RemoveUser (userID int) error {
+	if !isValidInput(strconv.Itoa(userID)) {
+		return errors.New("invalid input: contains illegal characters")
+	}
+
+	result, err := db.Exec("DELETE FROM userLogin WHERE userID = ?", userID)
+	if err != nil {
+		return fmt.Errorf("failed to delete user: %w", err)
+	}
+
+	rowsAffected, err := result.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("failed to get rows affected: %w", err)
+	}
+
+	if rowsAffected == 0 {
+		return errors.New("user not found")
+	}
+
+	return nil
+}
+
 func GetUserByUsername(username string) (*User, error) {
 	if !isValidInput(username) {
 		return nil, errors.New("invalid input: contains illegal characters")