review(track0): async ContextMenu OnClick + keyboard-⋯ anchoring + focus-return; discovery-driven DriverTypeNames guard; CSV round-trip comment

Wave-0 reviewer findings (no Critical/High):
- T0-1 M: ContextMenuItem.OnClick Action→Func<Task> (kills async-void at menu call sites Wave A/B/C need); keyboard-activated ⋯ now anchors below the button instead of viewport (0,0); focus returns to trigger on close; backdrop closes on native right-click too.
- T0-3 M: guard test now discovers *DriverFactoryExtensions.Register by convention from the deployed driver assemblies instead of a hand-copied list, so a future driver lacking a constant is actually caught.
- T0-2 L: corrected the round-trip 'sole non-round-trippable shape' comment (any table whose final row is a lone empty field).

Claude-Session: https://claude.ai/code/session_01LVneM3eh1UtJxEisFXgmox

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Dev/ContextMenuDemo.razor

@@ -31,5 +31,9 @@
         new() { Label = "Delete", Icon = "🗑️", Disabled = true, OnClick = () => Set("Delete") },
     };
 
-    private void Set(string action) => _lastAction = action;
+    private Task Set(string action)
+    {
+        _lastAction = action;
+        return Task.CompletedTask;
+    }
 }