feat(proxy): add proxy management endpoint and proxy creation API

- Implement new endpoint for creating frpc proxy configurations
- Add DBQueryFrpcInstanceByID function to fetch instances by ID
- Move proxy generation logic to separate function in frpcProxyAct.go
- Update API documentation with new proxy creation endpoint

database.go

@@ -361,6 +361,18 @@ func DBAddFrpcInstance(instance FrpcInstance) error {
 	return nil
 }
 
+func DBQueryFrpcInstanceByID(instanceID int) (FrpcInstance, error) {
+	var instance FrpcInstance
+	var createdAtStr string
+	err := frpcDB.QueryRow("SELECT id, userID, name, serverAddr, serverPort, auth_method, bootAtStart, runUser, configPath, createdAt FROM frpcInstances WHERE id = ?", instanceID).Scan(
+		&instance.ID, &instance.UserID, &instance.Name, &instance.ServerAddr, &instance.ServerPort, &instance.AuthMethod, &instance.BootAtStart, &instance.RunUser, &instance.ConfigPath, &createdAtStr)
+	if err != nil {
+		return instance, fmt.Errorf("failed to query frpc instance: %w", err)
+	}
+	instance.CreatedAt, _ = time.Parse(time.RFC3339, createdAtStr)
+	return instance, nil
+}
+
 func DBQueryFrpcInstance(userID int, instanceName string) (FrpcInstance, error) {
 	var instance FrpcInstance
 	var createdAtStr string