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/DeadlineList.tsx

@@ -54,12 +54,12 @@ export function DeadlineList() {
 
   const { data: deadlines, isLoading } = useQuery({
     queryKey: ["deadlines"],
-    queryFn: () => api.get<Deadline[]>("/api/deadlines"),
+    queryFn: () => api.get<Deadline[]>("/deadlines"),
   });
 
   const { data: cases } = useQuery({
     queryKey: ["cases"],
-    queryFn: () => api.get<Case[]>("/api/cases"),
+    queryFn: () => api.get<Case[]>("/cases"),
   });
 
   const completeMutation = useMutation({