feat(frontend): Inventar (Modul 24)

/equipment, /equipment/new, /equipment/:id mit Zustandsaenderung.
statusTone()-Helper um Equipment-Zustaende (NEW/GOOD/WORN/DEFECTIVE)
erweitert, Nav-Dropdown um Inventar ergaenzt.

ApiCore-Frontend/src/app/(app)/layout.tsx

@@ -32,6 +32,7 @@ const PRIMARY_LINKS = [
 const MORE_LINKS = [
   { label: "Produkte", href: "/products" },
   { label: "Abfüllungen", href: "/bottling/new" },
+  { label: "Inventar", href: "/equipment" },
 ];
 
 const ADMIN_LINKS = [