Add study activity tracking and refresh class header UI

src/lib/activityClient.ts

@@ -0,0 +1,9 @@
+import type { StudyActivityType } from "@/lib/validation/activitySchemas";
+
+export function recordStudyActivity(type: StudyActivityType) {
+  return fetch("/api/activity", {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({ type }),
+  });
+}

src/lib/validation/activitySchemas.ts

@@ -0,0 +1,7 @@
+import { z } from "zod";
+
+export const studyActivitySchema = z.object({
+  type: z.enum(["FLASHCARD", "QUIZ_QUESTION"]),
+});
+
+export type StudyActivityType = z.infer<typeof studyActivitySchema>["type"];