feat: dodaj display_code polje za putne naloge (MT070626 format)

- Dodano polje 'display_code' na WorkOrder model (format: 2 inicijala + ddmmyy)
- Migracije za kreiranje polja i backfill postojećih naloga
- Ažuriran WorkOrderSerializer za validaciju i serijalizaciju display_code
- Backend tasks za auto-generiranje display_code pri kreiranju
- Frontend komponente ažurirane za prikaz display_code umjesto UUID:
  * FleetDashboardShell tablica putnih naloga
  * WorkOrderDetailModal
  * TaskCreateModal
  * Sve PDF stranice
- displayIds.js utility za formatiranjeDisplay ID-eva
- Admin interface prikazuje display_code

frontend/src/layouts/Layout.astro

@@ -52,7 +52,7 @@ const isDev = import.meta.env.DEV;
     <div class="absolute inset-0 bg-[linear-gradient(to_right,var(--color-text-main)_0.03_1px,transparent_1px),linear-gradient(to_bottom,var(--color-text-main)_0.03_1px,transparent_1px)] bg-[size:64px_64px] opacity-[0.4] dark:opacity-[0.02] pointer-events-none z-0"></div>
 
     {!isAuthPage && <NetworkGuard client:only="preact" />}
-    <Toast client:load />
+    <Toast client:only="preact" />
     {!isAuthPage && isDev && <ToastTrigger client:load />}
     {!isAuthPage && <Navbar client:load minimal={minimalNav} />}