Refactor to multi-category catalog with polished light mode

- Restructure from single filament table to multi-category product catalog
  (filamenti, stampaci, ploce, mlaznice, delovi, oprema)
- Add shared layout components (SiteHeader, SiteFooter, CategoryNav, Breadcrumb)
- Add reusable UI primitives (Badge, Button, Card, Modal, PriceDisplay, EmptyState)
- Add catalog components (CatalogPage, ProductTable, ProductGrid, FilamentCard, ProductCard)
- Add admin dashboard with sidebar navigation and category management
- Add product API endpoints and database migrations
- Add SEO pages (politika-privatnosti, uslovi-koriscenja, robots.txt, sitemap.xml)
- Fix light mode: gradient text contrast, category nav accessibility,
  surface tokens, card shadows, CTA section theming

app/upadaj/dashboard/layout.tsx

@@ -0,0 +1,8 @@
+'use client';
+import { AdminLayout } from '@/src/components/layout/AdminLayout';
+import { usePathname } from 'next/navigation';
+
+export default function DashboardLayout({ children }: { children: React.ReactNode }) {
+  const pathname = usePathname();
+  return <AdminLayout currentPath={pathname}>{children}</AdminLayout>;
+}