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/Configs/Create/CreateVpnConfigCommandHandler.cs

@@ -36,7 +36,7 @@ public sealed class CreateVpnConfigCommandHandler(
         if (node is null || !node.IsEnabled)
             return Result.Failure<VpnConfigDto>(ConfigErrors.NodeDisabled);
 
-        var config = VpnConfig.Create(userId, inbound.Id, inbound.Protocol, command.Label, command.DeviceLimit ?? 0);
+        var config = VpnConfig.Create(userId, inbound.Id, inbound.Protocol, command.Label);
 
         var reserveResult = await ReserveQuotaSlotAsync(userId, profile.MaxConfigs, config, cancellationToken);
         if (!reserveResult.IsSuccess)
@@ -44,7 +44,7 @@ public sealed class CreateVpnConfigCommandHandler(
 
         var addResult = await gateway.AddClientAsync(
             node, inbound.RemoteInboundId, inbound.Protocol, config.ClientEmail,
-            config.Label ?? config.ClientEmail, config.DeviceLimit, cancellationToken);
+            config.Label ?? config.ClientEmail, cancellationToken);
 
         if (!addResult.IsSuccess)
         {