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.Api/Endpoints/ConfigEndpoints.cs

@@ -44,14 +44,14 @@ public static class ConfigEndpoints
 
     private static async Task<IResult> CreateConfig(CreateConfigBody body, ISender sender, CancellationToken cancellationToken)
     {
-        var command = new CreateVpnConfigCommand(body.InboundId, body.Label, body.DeviceLimit);
+        var command = new CreateVpnConfigCommand(body.InboundId, body.Label);
         var result = await sender.Send(command, cancellationToken);
         return result.ToHttpResult();
     }
 
     private static async Task<IResult> EditConfig(Guid id, EditConfigBody body, ISender sender, CancellationToken cancellationToken)
     {
-        var command = new EditVpnConfigCommand(id, body.Label, body.DeviceLimit);
+        var command = new EditVpnConfigCommand(id, body.Label);
         var result = await sender.Send(command, cancellationToken);
         return result.ToHttpResult();
     }
@@ -89,9 +89,9 @@ public static class ConfigEndpoints
     }
 }
 
-public sealed record CreateConfigBody(Guid InboundId, string? Label, int? DeviceLimit);
+public sealed record CreateConfigBody(Guid InboundId, string? Label);
 
-public sealed record EditConfigBody(string? Label, int? DeviceLimit);
+public sealed record EditConfigBody(string? Label);
 
 public sealed record ConfigLinkResponseDto(string ConnectionString, string SubscriptionUrl);