Fix: re-organized dialog and notification z-indices

- Notifications and toasts now appear higher than dialogs when appearing together
- Standardized dialog z-index
- Added documentation for z-index guide

src/App.vue

@@ -4,7 +4,7 @@
   <!-- Messages in the upper-right - https://github.com/emmanuelsw/notiwind -->
   <NotificationGroup group="alert">
     <div
-      class="fixed z-[90] top-[max(1rem,env(safe-area-inset-top))] right-4 left-4 sm:left-auto sm:w-full sm:max-w-sm flex flex-col items-start justify-end"
+      class="fixed z-[120] top-[max(1rem,env(safe-area-inset-top))] right-4 left-4 sm:left-auto sm:w-full sm:max-w-sm flex flex-col items-start justify-end"
     >
       <Notification
         v-slot="{ notifications, close }"