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/deadlines/DeadlineCalculator.tsx

@@ -39,14 +39,14 @@ export function DeadlineCalculator() {
 
   const { data: proceedingTypes, isLoading: typesLoading } = useQuery({
     queryKey: ["proceeding-types"],
-    queryFn: () => api.get<ProceedingType[]>("/api/proceeding-types"),
+    queryFn: () => api.get<ProceedingType[]>("/proceeding-types"),
   });
 
   const calculateMutation = useMutation({
     mutationFn: (params: {
       proceeding_type: string;
       trigger_event_date: string;
-    }) => api.post<CalculateResponse>("/api/deadlines/calculate", params),
+    }) => api.post<CalculateResponse>("/deadlines/calculate", params),
   });
 
   function handleCalculate(e: React.FormEvent) {