feat(userMgr): add list users endpoint

Add new endpoint `/userMgr/list` to retrieve all users with superuser permission. Includes handler implementation, database query function, and API documentation update.

database.go

@@ -198,24 +198,6 @@ func UpdateUserType(userID int, newType string) error {
 	return nil
 }
 
-func DeleteUser(userID int) error {
-	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 GetNextAvailableUserID() (int, error) {
 	var maxID int
 	err := db.QueryRow("SELECT COALESCE(MAX(userID), 0) FROM userLogin").Scan(&maxID)
@@ -309,6 +291,28 @@ func InitUserDatabase(dbPath string) error {
 	return nil
 }
 
+func DBQueryUsers() ([]User, error) { // List all users
+	rows, err := db.Query("SELECT userID, username, type FROM userLogin")
+	if err != nil {
+		return nil, fmt.Errorf("failed to query users: %w", err)
+	}
+	defer rows.Close()
+	var users []User
+	for rows.Next() {
+		var user User
+		if err := rows.Scan(&user.UserID, &user.Username, &user.Type); err != nil {
+			return nil, fmt.Errorf("failed to scan user: %w", err)
+		}
+		users = append(users, user)
+	}
+
+	if err = rows.Err(); err != nil {
+		return nil, fmt.Errorf("rows error: %w", err)
+	}
+
+	return users, nil
+}
+
 func DBAddFrpcInstance(instance FrpcInstance) error {
 	_, err := frpcDB.Exec("INSERT INTO frpcInstances (userID, name, serverAddr, serverPort, auth_method, bootAtStart, runUser, configPath, createdAt) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)",
 		instance.UserID, instance.Name, instance.ServerAddr, instance.ServerPort, instance.AuthMethod, instance.BootAtStart, instance.RunUser, instance.ConfigPath, time.Now().Format(time.RFC3339))