docs: add XML doc comments to Core public API and remove CS1591 suppression

- Add missing XML doc comments to all public types and members in
  PSProxmoxVE.Core (Authentication, Exceptions, Models, Client)
- Remove CS1591 suppression from PSProxmoxVE.Core.csproj
- Build succeeds with 0 warnings

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

src/PSProxmoxVE.Core/Models/Vms/PveCloudInitConfig.cs

@@ -48,6 +48,7 @@ namespace PSProxmoxVE.Core.Models.Vms
         [JsonProperty("cicustom")]
         public string? CiCustom { get; set; }
 
+        /// <inheritdoc />
         public override string ToString() =>
             $"CloudInit: User={CiUser ?? "N/A"} | IP0={IpConfig0 ?? "N/A"} | NS={Nameserver ?? "N/A"}";
     }

src/PSProxmoxVE.Core/Models/Vms/PveGuestIpAddress.cs

@@ -23,5 +23,6 @@ public class PveGuestIpAddress
     [JsonProperty("prefix")]
     public int Prefix { get; set; }
 
+    /// <inheritdoc />
     public override string ToString() => $"{Address}/{Prefix} ({Type})";
 }

src/PSProxmoxVE.Core/Models/Vms/PveGuestNetworkInterface.cs

@@ -23,6 +23,7 @@ public class PveGuestNetworkInterface
     [JsonProperty("ip-addresses")]
     public PveGuestIpAddress[] IpAddresses { get; set; } = System.Array.Empty<PveGuestIpAddress>();
 
+    /// <inheritdoc />
     public override string ToString()
     {
         var ips = IpAddresses.Length > 0

src/PSProxmoxVE.Core/Models/Vms/PveTaskLog.cs

@@ -16,6 +16,7 @@ namespace PSProxmoxVE.Core.Models.Vms
         [JsonProperty("t")]
         public string Text { get; set; } = string.Empty;
 
+        /// <inheritdoc />
         public override string ToString() => $"{LineNumber,4}: {Text}";
     }
 }