docs: add hash table operations SVG, prefix‑sum PNG, and redirect for LC 974

apps/docs/redirects.ts

@@ -76,6 +76,7 @@ export default [
   { from: "/853", to: "/monotonic-stack/car-fleet" },
   { from: "/875", to: "/binary-search/koko-eating-bananas" },
   { from: "/973", to: "/heap-priority-queue/k-closest-points-to-origin" },
+  { from: "/974", to: "/prefix-sum/subarray-sums-divisible-by-k" },
   { from: "/977", to: "/two-pointers/squares-of-a-sorted-array" },
   { from: "/994", to: "/graph-bfs/rotting-oranges" },
   { from: "/1143", to: "/multi-d-grid-dp/longest-common-subsequence" },