fix: remove defunct DELETE /access/ticket call and gain -Session parameter

Disconnect-PveServer was calling DELETE /access/ticket, an endpoint that does
not exist in the PVE API spec. The call always failed but errors were swallowed,
so the cmdlet succeeded while claiming server-side invalidation occurred.

Rebase on PveCmdletBase to gain the -Session parameter, making explicit session
disconnection possible (the cmdlet previously only worked with the active
session). Update help text to clarify that PVE tickets expire server-side after
two hours and cannot be revoked.

Remove the DELETE call entirely — tickets are stateless and expire on their own.
Clear ModuleState.ActiveSession only when disconnecting the active session
(no -Session given) or when explicitly disconnecting the active session.

tests/PSProxmoxVE.Tests/Connection/Disconnect-PveServer.Tests.ps1

@@ -38,6 +38,10 @@ Describe 'Disconnect-PveServer' {
             # attribute is present by confirming ShouldProcess support is enabled.
             $script:Cmd.Parameters.ContainsKey('WhatIf') | Should -BeTrue
         }
+
+        It 'Should expose -Session parameter' {
+            $script:Cmd.Parameters.ContainsKey('Session') | Should -BeTrue
+        }
     }
 
     Context 'Behaviour when no session is active' {
@@ -53,4 +57,12 @@ Describe 'Disconnect-PveServer' {
             { Disconnect-PveServer -WhatIf -ErrorAction Stop } | Should -Not -Throw
         }
     }
+
+    Context 'Active session lifecycle' {
+        It 'Should clear active session when disconnected without explicit -Session' {
+            Disconnect-PveServer -Confirm:$false -ErrorAction SilentlyContinue
+            $Module = Get-Module PSProxmoxVE
+            $Module.PrivateData.ModuleState.ActiveSession | Should -BeNullOrEmpty
+        }
+    }
 }