feat(frontend): add progress tracking

frontend/src/components/questions/completion-indicator.tsx

@@ -0,0 +1,26 @@
+"use client";
+
+import { useState, useEffect } from "react";
+import { CheckCircle } from "lucide-react";
+import { isQuestionCompleted } from "@/lib/progress";
+
+interface CompletionIndicatorProps {
+  slug: string;
+}
+
+export function CompletionIndicator({ slug }: CompletionIndicatorProps) {
+  const [completed, setCompleted] = useState(false);
+
+  useEffect(() => {
+    setCompleted(isQuestionCompleted(slug));
+  }, [slug]);
+
+  if (!completed) return null;
+
+  return (
+    <CheckCircle
+      className="h-4 w-4 text-green-500 flex-shrink-0"
+      aria-label="Completed"
+    />
+  );
+}