fix: remove /api/ double-prefix from all frontend API calls

Frontend api.ts baseUrl is already "/api", so paths like
"/api/cases" produced "/api/api/cases". Stripped the redundant
prefix from all component calls. Rewrite destination correctly
adds /api/ back for the Go backend.

frontend/src/components/appointments/AppointmentList.tsx

@@ -54,16 +54,16 @@ export function AppointmentList({ onEdit }: AppointmentListProps) {
 
   const { data: appointments, isLoading } = useQuery({
     queryKey: ["appointments"],
-    queryFn: () => api.get<Appointment[]>("/api/appointments"),
+    queryFn: () => api.get<Appointment[]>("/appointments"),
   });
 
   const { data: cases } = useQuery({
     queryKey: ["cases"],
-    queryFn: () => api.get<{ cases: Case[]; total: number }>("/api/cases"),
+    queryFn: () => api.get<{ cases: Case[]; total: number }>("/cases"),
   });
 
   const deleteMutation = useMutation({
-    mutationFn: (id: string) => api.delete(`/api/appointments/${id}`),
+    mutationFn: (id: string) => api.delete(`/appointments/${id}`),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["appointments"] });
       toast.success("Termin geloscht");