Phase 2: learning engine — history, SRS review, mistakes, stats, exam, reminders

Answer history and schedules
- Every answer is recorded (deck, activity, topic, correct/wrong, time)
  in a versioned IndexedDB log (freezmo-learning v1, stores answers +
  srs), mirrored in memory for synchronous React reads and capped at
  20k answers (oldest pruned). StudyFeed records as it grades.
- Light SM-2 schedule per activity: 1 day, 3 days, then interval x
  ease; wrong answers return in ten minutes with the ease nudged down.

Review, mistakes, stats
- Library 'Smart review' card: due count, mistakes count (latest
  answer wrong — clears itself when answered correctly), today's goal
  progress. Review sessions freeze their item list at start.
- New /review (due across decks, ?mistakes=1 global or ?deck= per
  deck) built on a shared SessionFeed with the study feed's snap/keyboard
  mechanics, wake lock and a results slide.
- New /stats: day streak, five-week calendar, accuracy per subject and
  per deck, weakest topics (>=3 answers), daily-goal progress.
- Daily goal configurable in Settings (10/20/30/50).

Exam mode
- New /exam: pick decks, question count, optional timer; no hints
  (a NoHints context hides hint rows and the self-check escape);
  results with score, per-deck and per-topic breakdown; wrong answers
  land in the mistakes set through the normal history.

Reminders (conditional)
- VAPID-gated: GET/POST/DELETE /api/push and POST /api/push/test with
  the standard route pattern, RATE_LIMIT_PUSH, zod, auth before body.
  Subscriptions stored server-side as endpoint + keys only (PUSH_DIR).
  UI hidden entirely without keys; iOS install note; service worker
  push/notificationclick handlers; scripts/send-reminders.mjs for a
  cron/systemd timer; web-push added as the one server dependency.

Verified: new phase-2 suite 42/42 (history/SRS shapes from a real study
run, mistakes clearing, review session, stats math, exam timer and
breakdowns, VAPID-less hidden state plus the configured
subscribe/validate/test/delete path against a second instance) plus
regression 74/74, mobile 52/52, wizard 80/80, declutter 116/116,
animation 8/8, native 35/35, phase1 38/38, i18n 25/25. Key parity
709/709. Lint + build clean. SW freezmo-v26.

components/DataSection.tsx

@@ -50,9 +50,9 @@ export function DataSection() {
     if (fileRef.current) fileRef.current.value = "";
   };
 
-  const apply = (mode: "merge" | "replace") => {
+  const apply = async (mode: "merge" | "replace") => {
     if (!pending) return;
-    const done = applyImport(pending.backup, mode);
+    const done = await applyImport(pending.backup, mode);
     setNotice(t("settings.importDone", { decks: done.decks, homework: done.homework }));
     reset();
   };
@@ -69,7 +69,7 @@ export function DataSection() {
       <p className="text-[11.5px] leading-relaxed text-[var(--text-subtle)]">{t("settings.dataNote")}</p>
 
       <div className="grid gap-2">
-        <Button size="sm" variant="secondary" className="touch-target w-full" onClick={() => downloadBackup()}>
+        <Button size="sm" variant="secondary" className="touch-target w-full" onClick={() => void downloadBackup()}>
           {t("settings.exportAll")}
         </Button>
         <Button size="sm" variant="secondary" className="touch-target w-full" onClick={() => fileRef.current?.click()}>
@@ -97,10 +97,10 @@ export function DataSection() {
           <p className="text-[11px] leading-relaxed text-[var(--text-subtle)]">{t("settings.importMergeNote")}</p>
           <p className="text-[11px] leading-relaxed text-[var(--text-subtle)]">{t("settings.importReplaceNote")}</p>
           <div className="flex flex-wrap gap-2">
-            <Button size="sm" onClick={() => apply("merge")}>
+            <Button size="sm" onClick={() => void apply("merge")}>
               {t("settings.importMerge")}
             </Button>
-            <Button size="sm" variant="danger" onClick={() => apply("replace")}>
+            <Button size="sm" variant="danger" onClick={() => void apply("replace")}>
               {t("settings.importReplace")}
             </Button>
             <Button size="sm" variant="ghost" onClick={reset}>