Lite and the Darling Viewer: 18 unguarded clipboard writes can crash the app when the clipboard is busy #4594

Every clipboard write in Lite and the Darling Viewer outside the shared plan viewer still calls Clipboard.SetText/SetDataObject unguarded. When another program holds the Windows clipboard, WPF throws COMException (CLIPBRD_E_CANT_OPEN), and in a click handler that ends the app.

#4582 (PR #4593) adds a guarded writer, ClipboardText.TrySetText in PerformanceMonitor.Ui, with the same bounded retry as the existing guarded reader. It routes the shared plan viewer, blocking chain, deadlock graph and grid-export copies through it. The same unguarded pattern remains at 18 sites:

• Lite: Helpers/ContextMenuHelper.cs (4, including the chart bitmap copy), Controls/ServerTab.CopyExport.cs, Controls/RecommendationsTab.xaml.cs (2), Windows/SettingsWindow.xaml.cs, Windows/AlertDetailWindow.xaml.cs, and Windows/EntraDeviceCodeWindow.xaml.cs.
• The Darling Viewer: MainWindow.xaml.cs (3), ViewerServerTab.CopyExport.cs, ViewerServerTab.ChartContextMenu.cs, SettingsWindow.xaml.cs (2), and AlertDetailWindow.xaml.cs.

The fix is mechanical: route each through ClipboardText.TrySetText (and a bitmap-capable overload for the chart copy), and pin with a census that no unguarded Clipboard.Set* call is left outside ClipboardText. deprecated/ is out of scope.

Found while porting erikdarlingdata/PerformanceStudio@7cd9218's clipboard guard for #4582. At 08f3e3c4e.