fix: address code review findings

cmd/api/handlers.go

@@ -429,16 +429,14 @@ func StationStatus(hc *HandlerContext, w http.ResponseWriter, r *http.Request) {
 // adminAuth checks authentication for admin endpoints.
 // Returns true if the request is authenticated, false otherwise.
 func adminAuth(hc *HandlerContext, w http.ResponseWriter, r *http.Request) bool {
-	// Check for admin API key in header
 	expectedAPIKey := os.Getenv("TRIP_PLANNER_ADMIN_API_KEY")
 	if expectedAPIKey == "" {
-		// Admin API key must be configured
-		http.Error(w, "unauthorized: admin API key not configured", http.StatusUnauthorized)
+		http.Error(w, "unauthorized", http.StatusUnauthorized)
 		return false
 	}
 	providedAPIKey := r.Header.Get("X-Admin-Api-Key")
 	if !hmac.Equal([]byte(providedAPIKey), []byte(expectedAPIKey)) {
-		http.Error(w, "unauthorized: invalid admin API key", http.StatusUnauthorized)
+		http.Error(w, "unauthorized", http.StatusUnauthorized)
 		return false
 	}
 	return true