Quizzes: To do = started but unfinished; durations roll into days

The To do tab now lists only quizzes you've started and not finished;
untouched ones stay under All. Quiz times show hours and days
(3h 20m, 2d 4h) instead of ever-growing minutes, and 59.96s no longer
prints as "60.0s".

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

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

@@ -57,7 +57,9 @@ export function QuizzesList() {
           ? true
           : filter === "done"
             ? q.my.state === "completed"
-            : q.my.state !== "completed",
+            : // To do: started but not finished. Untouched quizzes live
+              // under All.
+              q.my.state === "in_progress",
       ),
     [list, filter],
   );