feat: add parameter-level version warnings for named params from newer PVE

Warn (not block) when users pass named parameters that were added in
later PVE versions:
- Send-PveFile: -Checksum/-ChecksumAlgorithm require PVE 7.1
- New/Set-PveSdnSubnet: -DhcpRange requires PVE 8.1

These are warnings, not hard blocks — the parameter is still sent to
the API, which will either accept it or return its own error. This
only applies to named cmdlet parameters, not AdditionalConfig
pass-through hashtables.

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

src/PSProxmoxVE/Cmdlets/Network/NewPveSdnSubnetCmdlet.cs

@@ -45,6 +45,14 @@ namespace PSProxmoxVE.Cmdlets.Network
 
             var session = GetSession();
             RequireVersion(session, "SDN", 6, 2, 8, 0);
+
+            if (!string.IsNullOrEmpty(DhcpRange)
+                && session.ServerVersion != null && !session.ServerVersion.IsAtLeast(8, 1))
+            {
+                WriteWarning("The -DhcpRange parameter requires PVE 8.1 or later. "
+                    + $"Connected server is PVE {session.ServerVersion}. The parameter will be sent but may be ignored.");
+            }
+
             using var client = new PveHttpClient(session);
 
             WriteVerbose($"Creating SDN subnet '{Subnet}' on VNet '{Vnet}'...");

src/PSProxmoxVE/Cmdlets/Network/SetPveSdnSubnetCmdlet.cs

@@ -45,6 +45,14 @@ namespace PSProxmoxVE.Cmdlets.Network
 
             var session = GetSession();
             RequireVersion(session, "SDN", 6, 2, 8, 0);
+
+            if (!string.IsNullOrEmpty(DhcpRange)
+                && session.ServerVersion != null && !session.ServerVersion.IsAtLeast(8, 1))
+            {
+                WriteWarning("The -DhcpRange parameter requires PVE 8.1 or later. "
+                    + $"Connected server is PVE {session.ServerVersion}. The parameter will be sent but may be ignored.");
+            }
+
             var service = new NetworkService();
 
             WriteVerbose($"Updating SDN subnet '{Subnet}' on VNet '{Vnet}'...");

src/PSProxmoxVE/Cmdlets/Storage/SendPveFileCmdlet.cs

@@ -66,6 +66,14 @@ namespace PSProxmoxVE.Cmdlets.Storage
                 return;
 
             var session = GetSession();
+
+            if ((!string.IsNullOrEmpty(Checksum) || !string.IsNullOrEmpty(ChecksumAlgorithm))
+                && session.ServerVersion != null && !session.ServerVersion.IsAtLeast(7, 1))
+            {
+                WriteWarning("The -Checksum and -ChecksumAlgorithm parameters require PVE 7.1 or later. "
+                    + $"Connected server is PVE {session.ServerVersion}. The upload will proceed without checksum verification.");
+            }
+
             using var client = new PveHttpClient(session);
 
             WriteVerbose($"Uploading {fileName} to {Node}/{Storage} (content={ContentType})...");