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/mlaznice/layout.tsx

@@ -0,0 +1,18 @@
+import type { Metadata } from 'next';
+
+export const metadata: Metadata = {
+  title: 'Bambu Lab Nozzle i Hotend (Mlaznice/Dizne)',
+  description: 'Bambu Lab nozzle mlaznice i hotend za A1, P1, X1. Hardened steel, stainless steel dizne.',
+  openGraph: {
+    title: 'Bambu Lab Nozzle i Hotend (Mlaznice/Dizne) - Filamenteka',
+    description: 'Bambu Lab nozzle mlaznice i hotend za A1, P1, X1. Hardened steel, stainless steel dizne.',
+    url: 'https://filamenteka.rs/mlaznice',
+  },
+  alternates: {
+    canonical: 'https://filamenteka.rs/mlaznice',
+  },
+};
+
+export default function MlaznicaLayout({ children }: { children: React.ReactNode }) {
+  return <>{children}</>;
+}