feat: role-based permissions — owner/partner/associate/paralegal/secretary (P0)

frontend/src/app/(app)/cases/[id]/layout.tsx

@@ -13,6 +13,7 @@ import {
   Clock,
   FileText,
   Users,
+  UserCheck,
   StickyNote,
   AlertTriangle,
   ScrollText,
@@ -44,6 +45,7 @@ const TABS = [
   { segment: "fristen", label: "Fristen", icon: Clock },
   { segment: "dokumente", label: "Dokumente", icon: FileText },
   { segment: "parteien", label: "Parteien", icon: Users },
+  { segment: "mitarbeiter", label: "Mitarbeiter", icon: UserCheck },
   { segment: "notizen", label: "Notizen", icon: StickyNote },
   { segment: "protokoll", label: "Protokoll", icon: ScrollText },
 ] as const;
@@ -53,6 +55,7 @@ const TAB_LABELS: Record<string, string> = {
   fristen: "Fristen",
   dokumente: "Dokumente",
   parteien: "Parteien",
+  mitarbeiter: "Mitarbeiter",
   notizen: "Notizen",
   protokoll: "Protokoll",
 };