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/VpnConfigDto.cs

@@ -8,10 +8,10 @@ namespace PnvPanel.Application.Configs;
 /// детали 3x-ui в этот DTO не попадают (см. domain-model.md).
 /// </summary>
 public sealed record VpnConfigDto(
-    Guid Id, string? Label, VpnProtocol Protocol, string Location, int DeviceLimit,
+    Guid Id, string? Label, VpnProtocol Protocol, string Location,
     long UsedUpBytes, long UsedDownBytes, DateTimeOffset? ExpiresAt, ConfigStatus Status, DateTimeOffset CreatedAt)
 {
     public static VpnConfigDto FromDomain(VpnConfig config, Inbound inbound) => new(
-        config.Id, config.Label, config.Protocol, inbound.DisplayName ?? inbound.Remark, config.DeviceLimit,
+        config.Id, config.Label, config.Protocol, inbound.DisplayName ?? inbound.Remark,
         config.UsedUpBytes, config.UsedDownBytes, config.ExpiresAt, config.Status, config.CreatedAt);
 }