Remove nominative testing, add hideable hints and week streak dots

- Remove the Nominativ level and drop nominative-case testing from mixed/
  possessive/pronoun levels (nominative kept only in reference charts)
- Add persistent hide/show toggles on the two giveaway hint lines in
  practice (noun gender, case/preposition info); state persists in localStorage
- De-spoil "Wechsel im Kontext": remove motion/location hint from answer
  buttons; put sentence translation + preposition meaning behind a toggle
- Add a 7-day practice-history dot strip beside the streak counter
- Extend engine + tests (61 vitest tests)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/engine.test.js

@@ -4,7 +4,7 @@ import {
   NOUNS, nounForm, LEVELS, CONTRACTIONS, CONTRACTABLE, CHUNK_PREPS,
   POSS_ENDINGS, combinePoss, PRONOUNS, VERBS, PREP_FRAMES,
   createSession, gen, genContractionContextQ, newState, buildChunkChoices,
-  bumpStreak, currentStreak,
+  bumpStreak, currentStreak, weekDots,
 } from './engine.js';
 
 const runSession = (levelId, n) => {
@@ -238,9 +238,22 @@ describe('pronoun questions', () => {
   it.each([14, 15, 16, 17])('level %s: answer matches the pronoun table', (id) => {
     for (const q of runSession(id, 200)) {
       const p = PRONOUNS.find(x => x.key === q.pronKey);
-      const expected = p[{nominative:'nom',accusative:'acc',dative:'dat'}[q.cas]];
-      const want = q.cas === 'nominative' ? expected.charAt(0).toUpperCase() + expected.slice(1) : expected;
-      expect(q.ans).toBe(want);
+      expect(q.ans).toBe(p[{accusative:'acc',dative:'dat'}[q.cas]]);
+    }
+  });
+});
+
+// ── Nominative is never tested ──────────────────────────────
+
+describe('no nominative anywhere', () => {
+  it('no level tests the nominative — you already know der/die/das', () => {
+    expect(LEVELS.some(l => l.name === 'Nominativ')).toBe(false);
+    for (const lv of LEVELS) {
+      if (lv.cases) expect(lv.cases, `level ${lv.id} still lists nominative`).not.toContain('nominative');
+      for (const q of runSession(lv.id, 150)) {
+        if (q.cas) expect(q.cas, `level ${lv.id} generated a nominative question`).not.toBe('nominative');
+        expect(q.ans).not.toBe('nominative');
+      }
     }
   });
 });
@@ -289,6 +302,29 @@ describe('streaks', () => {
     expect(st.streak).toBe(10);
   });
 
+  it('records practice days and prunes old ones', () => {
+    let st = bumpStreak({ streak: 0, ld: null }, '2026-07-01');
+    expect(st.days['2026-07-01']).toBe(true);
+    st = bumpStreak(st, '2026-07-01'); // same day, already recorded
+    expect(Object.keys(st.days).length).toBe(1);
+    st = bumpStreak(st, '2026-07-02');
+    expect(st.days['2026-07-01']).toBe(true);
+    expect(st.days['2026-07-02']).toBe(true);
+    st = bumpStreak(st, '2026-07-20'); // far in the future → old days pruned
+    expect(st.days['2026-07-01']).toBeUndefined();
+    expect(st.days['2026-07-20']).toBe(true);
+  });
+
+  it('weekDots reports the last 7 days, today last', () => {
+    const st = { days: { '2026-07-10': true, '2026-07-12': true, '2026-07-14': true } };
+    const dots = weekDots(st, '2026-07-14');
+    expect(dots.length).toBe(7);
+    expect(dots[0].date).toBe('2026-07-08');
+    expect(dots[6].date).toBe('2026-07-14');
+    expect(dots[6].isToday).toBe(true);
+    expect(dots.map(d => d.practiced)).toEqual([false, false, true, false, true, false, true]);
+  });
+
   it('displays 0 once the streak has lapsed, without needing a new answer', () => {
     const st = { streak: 7, ld: '2026-07-01' };
     expect(currentStreak(st, '2026-07-01')).toBe(7);