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/StudyFeed.tsx

@@ -9,6 +9,7 @@ import { celebrate } from "@/lib/confetti";
 import { ApiError, generateDeck } from "@/lib/client-api";
 import { materialiseActivities } from "@/lib/deck-ops";
 import { haptic } from "@/lib/haptics";
+import { recordAnswer } from "@/lib/history";
 import { useI18n } from "@/lib/i18n";
 import type { Activity, Deck } from "@/lib/schemas";
 import { recordAttempt, upsertDeck } from "@/lib/storage";
@@ -124,6 +125,15 @@ export function StudyFeed({ deck }: { deck: Deck }) {
         if (current[activity.id]) return current; // first answer counts
         return { ...current, [activity.id]: { correct, userAnswer: meta?.userAnswer } };
       });
+      // Every answer feeds the history, the SRS schedule and the mistakes set.
+      recordAnswer({
+        deckId: currentDeck.id,
+        deckTitle: currentDeck.title,
+        activityId: activity.id,
+        type: activity.type,
+        topic: activity.topic,
+        correct,
+      });
       if (correct) {
         haptic("success");
         const nextStreak = streak + 1;
@@ -136,7 +146,7 @@ export function StudyFeed({ deck }: { deck: Deck }) {
         setStreak(0);
       }
     },
-    [streak],
+    [currentDeck.id, currentDeck.title, streak],
   );
 
   const missed = useMemo(