Add close button to UI toasts (#28246)

This commit tweaks the Toaster element to include a close button.

These toasts often cover other UI elements like the model selector, and
this change avoids having to wait for them to disappear on their own
(e.g. after a load failure).

tools/ui/src/routes/+layout.svelte

@@ -335,7 +335,7 @@
 
 	<ModeWatcher />
 
-	<Toaster richColors />
+	<Toaster closeButton richColors />
 </Tooltip.Provider>
 
 <!-- PWA update prompt + version -->