fix: use SecureString for guest password, validate Pool/CephPool conflict

Set-PveVmGuestPassword now accepts SecureString instead of plain string for
the -Password parameter, matching the established pattern in Set-PvePassword.
The password is converted via Marshal and zeroed from memory after use.

New-PveStorage now validates that -Pool and -CephPool cannot both be specified,
since both mapped to the same API key and CephPool silently overwrote Pool.

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

src/PSProxmoxVE/Cmdlets/Storage/NewPveStorageCmdlet.cs

@@ -15,7 +15,7 @@ namespace PSProxmoxVE.Cmdlets.Storage
     /// </summary>
     [Cmdlet(VerbsCommon.New, "PveStorage", SupportsShouldProcess = true)]
     [OutputType(typeof(PveStorage))]
-    public class NewPveStorageCmdlet : PveCmdletBase
+    public sealed class NewPveStorageCmdlet : PveCmdletBase
     {
         /// <summary>The unique storage identifier/name.</summary>
         [Parameter(Mandatory = true, Position = 0, HelpMessage = "The storage pool name.")]
@@ -80,6 +80,14 @@ namespace PSProxmoxVE.Cmdlets.Storage
             if (!ShouldProcess(Storage, "Create PVE Storage"))
                 return;
 
+            if (!string.IsNullOrEmpty(Pool) && !string.IsNullOrEmpty(CephPool))
+            {
+                ThrowTerminatingError(new ErrorRecord(
+                    new PSArgumentException("Pool and CephPool cannot both be specified. Use Pool for ZFS pools or CephPool for Ceph/RBD pools."),
+                    "PoolConflict", ErrorCategory.InvalidArgument, null));
+                return;
+            }
+
             var session = GetSession();
             using var client = new PveHttpClient(session);
 

src/PSProxmoxVE/Cmdlets/Vms/SetPveVmGuestPasswordCmdlet.cs

@@ -1,4 +1,6 @@
 using System.Management.Automation;
+using System.Runtime.InteropServices;
+using System.Security;
 using PSProxmoxVE.Core.Services;
 
 namespace PSProxmoxVE.Cmdlets.Vms
@@ -12,6 +14,7 @@ namespace PSProxmoxVE.Cmdlets.Vms
     /// </para>
     /// </summary>
     [Cmdlet(VerbsCommon.Set, "PveVmGuestPassword", SupportsShouldProcess = true)]
+    [OutputType(typeof(void))]
     public sealed class SetPveVmGuestPasswordCmdlet : PveCmdletBase
     {
         /// <summary>The Proxmox VE node name.</summary>
@@ -33,7 +36,7 @@ namespace PSProxmoxVE.Cmdlets.Vms
         /// <para type="description">The new password for the user.</para>
         /// </summary>
         [Parameter(Mandatory = true, HelpMessage = "The new password.")]
-        public string Password { get; set; } = string.Empty;
+        public SecureString Password { get; set; } = new SecureString();
 
         /// <summary>
         /// <para type="description">When specified, indicates the password is already in crypted/hashed format.</para>
@@ -48,9 +51,20 @@ namespace PSProxmoxVE.Cmdlets.Vms
 
             var session = GetSession();
 
+            var ptr = Marshal.SecureStringToGlobalAllocUnicode(Password);
+            string plainPassword;
+            try
+            {
+                plainPassword = Marshal.PtrToStringUni(ptr) ?? string.Empty;
+            }
+            finally
+            {
+                Marshal.ZeroFreeGlobalAllocUnicode(ptr);
+            }
+
             WriteVerbose($"Setting password for user '{Username}' on VM {VmId} via guest agent...");
             var service = new VmService();
-            service.SetGuestPassword(session, Node, VmId, Username, Password, Crypted.IsPresent);
+            service.SetGuestPassword(session, Node, VmId, Username, plainPassword, Crypted.IsPresent);
         }
     }
 }