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/Users/PveGroup.cs

@@ -1,4 +1,3 @@
-using System.Text.Json.Serialization;
 using Newtonsoft.Json;
 
 namespace PSProxmoxVE.Core.Models.Users;
@@ -9,22 +8,18 @@ namespace PSProxmoxVE.Core.Models.Users;
 public class PveGroup
 {
     /// <summary>The unique group identifier.</summary>
-    [JsonPropertyName("groupid")]
     [JsonProperty("groupid")]
     public string GroupId { get; set; } = string.Empty;
 
     /// <summary>Optional comment/description for the group.</summary>
-    [JsonPropertyName("comment")]
     [JsonProperty("comment")]
     public string? Comment { get; set; }
 
     /// <summary>Comma-separated list of user IDs that belong to this group.</summary>
-    [JsonPropertyName("users")]
     [JsonProperty("users")]
     public string? Users { get; set; }
 
     /// <summary>Array of member user IDs. Populated when available.</summary>
-    [JsonPropertyName("members")]
     [JsonProperty("members")]
     public string[]? Members { get; set; }