Standardise frontend hook fetch error handling and mark Task 12 done

frontend/src/hooks/useMapColorThresholds.ts

@@ -1,5 +1,6 @@
 import { useCallback, useEffect, useState } from "react";
 import { fetchMapColorThresholds, updateMapColorThresholds } from "../api/config";
+import { handleFetchError } from "../utils/fetchError";
 import type {
   MapColorThresholdsResponse,
   MapColorThresholdsUpdate,
@@ -26,7 +27,7 @@ export function useMapColorThresholds(): UseMapColorThresholdsResult {
       const data = await fetchMapColorThresholds();
       setThresholds(data);
     } catch (err: unknown) {
-      setError(err instanceof Error ? err.message : "Failed to fetch map color thresholds");
+      handleFetchError(err, setError, "Failed to fetch map color thresholds");
     } finally {
       setLoading(false);
     }