refactor: remove redundant System.Text.Json attributes from models

The codebase uses Newtonsoft.Json (JObject.Parse + ToObject<T>) exclusively.
Removed all [JsonPropertyName] attributes and [System.Text.Json.Serialization.
JsonIgnore] attributes from 41 model files, along with the now-unused
using System.Text.Json.Serialization imports. [JsonProperty] (Newtonsoft)
attributes remain as the sole serialization annotations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/PSProxmoxVE.Core/Models/Network/PveSdnSubnet.cs

@@ -1,4 +1,3 @@
-using System.Text.Json.Serialization;
 using Newtonsoft.Json;
 
 namespace PSProxmoxVE.Core.Models.Network;
@@ -13,56 +12,48 @@ public class PveSdnSubnet
     /// <summary>
     /// The subnet CIDR (e.g. "10.0.0.0/24" or "2001:db8::/64").
     /// </summary>
-    [JsonPropertyName("subnet")]
     [JsonProperty("subnet")]
     public string Subnet { get; set; } = string.Empty;
 
     /// <summary>
     /// The VNet this subnet belongs to.
     /// </summary>
-    [JsonPropertyName("vnet")]
     [JsonProperty("vnet")]
     public string? Vnet { get; set; }
 
     /// <summary>
     /// The gateway IP address for this subnet.
     /// </summary>
-    [JsonPropertyName("gateway")]
     [JsonProperty("gateway")]
     public string? Gateway { get; set; }
 
     /// <summary>
     /// Whether SNAT (source NAT) is enabled for this subnet.
     /// </summary>
-    [JsonPropertyName("snat")]
     [JsonProperty("snat")]
     public int? Snat { get; set; }
 
     /// <summary>
     /// The DNS zone name for this subnet.
     /// </summary>
-    [JsonPropertyName("dnszoneprefix")]
     [JsonProperty("dnszoneprefix")]
     public string? DnsZonePrefix { get; set; }
 
     /// <summary>
     /// The DHCP range configurations for automatic IP assignment.
     /// </summary>
-    [JsonPropertyName("dhcp-range")]
     [JsonProperty("dhcp-range")]
     public string[]? DhcpRanges { get; set; }
 
     /// <summary>
     /// The subnet type identifier used internally by PVE.
     /// </summary>
-    [JsonPropertyName("type")]
     [JsonProperty("type")]
     public string? Type { get; set; }
 
     /// <summary>
     /// Optional comment or description.
     /// </summary>
-    [JsonPropertyName("comments")]
     [JsonProperty("comments")]
     public string? Comments { get; set; }