Refactor VPN configuration handling to remove device limit management

- Updated the VPN configuration commands and handlers to eliminate the device limit parameter, simplifying the configuration process.
- Adjusted related API documentation to reflect the removal of device limit management, clarifying that this setting is now handled directly in the 3x-ui by node administrators.
- Enhanced the overall codebase by removing unnecessary device limit references across various components, ensuring a cleaner and more maintainable code structure.

backend/src/PnvPanel.Application/Common/Interfaces/IXuiPanelGateway.cs

@@ -27,7 +27,7 @@ public interface IXuiPanelGateway
     /// <summary>Возвращает ClientExternalId, присвоенный панелью (UUID для VLESS/VMess, пароль для Trojan/Shadowsocks).</summary>
     Task<Result<string>> AddClientAsync(
         Node node, string inboundRemoteId, VpnProtocol protocol, string clientEmail, string clientName,
-        int deviceLimit, CancellationToken cancellationToken);
+        CancellationToken cancellationToken);
 
     Task<Result> RemoveClientAsync(
         Node node, string inboundRemoteId, string clientExternalId, VpnProtocol protocol,
@@ -35,7 +35,7 @@ public interface IXuiPanelGateway
 
     Task<Result> UpdateClientAsync(
         Node node, string inboundRemoteId, string clientExternalId, VpnProtocol protocol,
-        string name, int deviceLimit, bool enable, CancellationToken cancellationToken);
+        string name, bool enable, CancellationToken cancellationToken);
 
     Task<Result<string>> BuildConnectionStringAsync(
         Node node, Inbound inbound, string clientExternalId, string clientName, string publicHost,