Quiz list: drill down by Books → book and Lectures → year

The All tab is now a click-through of category cards — Books, Lectures &
Conversations, Other quizzes — each opening its books or years, then the
quizzes themselves. Only categories with quizzes get a card. The position
and tab live in the URL (?in=books&book=bg, ?tab=todo), so refresh, Back
and shared links keep your place. Book quizzes list in chapter order.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/(app)/quizzes/quizzes-list.tsx

@@ -6,23 +6,37 @@
  * Reached from the Quizzes card on the search page. Quizzes are deliberately
  * not in search results: they're something to do, not something to look up.
  * Signed in only: visitors get the sign-in modal, and home if they dismiss it.
+ *
+ * The tab (?tab=todo) and, under All, the category you've drilled into
+ * (?in=books&book=bg) both live in the URL, so a refresh keeps your place.
  */
 
 import { useEffect, useMemo, useState } from "react";
+import { usePathname, useRouter, useSearchParams } from "next/navigation";
 import { useSignedInPage } from "@/components/auth/use-signed-in-page";
 import { quiz, type QuizCard } from "@/lib/quiz";
-import { groupQuizzes } from "@/lib/quiz-groups";
 import { QuizGrid } from "@/components/quiz/quiz-grid";
-import { GroupedQuizzes } from "@/components/quiz/grouped-quizzes";
+import { QuizBrowser } from "@/components/quiz/quiz-browser";
 import { cn } from "@/lib/utils";
 
 type Filter = "all" | "todo" | "done";
+const FILTERS: readonly Filter[] = ["all", "todo", "done"];
 
 export function QuizzesList() {
   const { user } = useSignedInPage();
   const userId = user?.id;
   const [list, setList] = useState<QuizCard[] | null>(null);
-  const [filter, setFilter] = useState<Filter>("all");
+  const params = useSearchParams();
+  const router = useRouter();
+  const pathname = usePathname();
+  const tabParam = params.get("tab") as Filter | null;
+  const filter: Filter =
+    tabParam && FILTERS.includes(tabParam) ? tabParam : "all";
+  // Switching tab starts that tab at its top; All is the bare URL.
+  const setFilter = (f: Filter) =>
+    router.replace(f === "all" ? pathname : `${pathname}?tab=${f}`, {
+      scroll: false,
+    });
 
   useEffect(() => {
     if (!userId) return;
@@ -99,7 +113,14 @@ export function QuizzesList() {
       ) : filter !== "all" ? (
         <QuizGrid quizzes={shown} />
       ) : (
-        <GroupedQuizzes sections={groupQuizzes(shown)} />
+        <QuizBrowser
+          quizzes={shown}
+          path={{
+            in: params.get("in"),
+            book: params.get("book"),
+            year: params.get("year"),
+          }}
+        />
       )}
     </main>
   );