Introduce overlay layering tokens and tests

torrent/beacon.html

@@ -290,7 +290,7 @@
     </main>
 
     <div
-      class="fixed inset-0 z-[60] flex items-center justify-center bg-overlay-muted/70 backdrop-blur-md"
+      class="ds-overlay-backdrop z-overlay-floating"
       data-beacon="processing-overlay"
       hidden
     >

torrent/ui/toastService.js

@@ -39,7 +39,7 @@ function ensureContainer(doc) {
       "fixed",
       "inset-x-0",
       "top-4",
-      "z-[70]",
+      "z-overlay-toast",
       "flex",
       "flex-col",
       "items-center",