feat(progress): spaced repetition dashboard

frontend/src/hooks/use-time-tracker.ts

@@ -0,0 +1,22 @@
+"use client";
+
+import { useEffect, useRef } from "react";
+import { timeTracker } from "@/lib/time-tracker";
+
+export function useTimeTracker(slug: string): number {
+  const elapsedRef = useRef(0);
+
+  useEffect(() => {
+    timeTracker.start(slug);
+
+    return () => {
+      elapsedRef.current = timeTracker.stop();
+    };
+  }, [slug]);
+
+  return elapsedRef.current;
+}
+
+export function getTimeTrackerElapsed(): number {
+  return timeTracker.getElapsedMs();
+}