articulate(app): port single-device word game from partiverse + tests

中英猜词派对 — 选主题 / 难度 / 词数 → 大字模式描述给队友猜，无 room / 无 ws。
15 个 preset 主题（wordlists 已在 scaffold 时就位）+ 3 档难度 + 已看词跨场
记忆（localStorage，cap 5000）+ Enter/Space/Esc 键盘。pickWords 优先未看过
再 fallback 见过的。logic 层 24 个 vitest（解析 / 抽词 / 确定性 rng）。

apps/articulate/frontend/src/__tests__/storage.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest'
+import { addSeen } from '../logic/storage'
+
+describe('addSeen', () => {
+  it('appends new keys to the end', () => {
+    expect(addSeen(['a', 'b'], ['c', 'd'])).toEqual(['a', 'b', 'c', 'd'])
+  })
+
+  it('deduplicates existing keys', () => {
+    expect(addSeen(['a', 'b'], ['b', 'c'])).toEqual(['a', 'b', 'c'])
+  })
+
+  it('handles all-duplicate addition', () => {
+    expect(addSeen(['a', 'b'], ['a', 'b'])).toEqual(['a', 'b'])
+  })
+
+  it('respects MAX_SEEN cap (5000) by trimming oldest', () => {
+    const existing = Array.from({ length: 5000 }, (_, i) => `k${i}`)
+    const out = addSeen(existing, ['new1', 'new2'])
+    expect(out).toHaveLength(5000)
+    expect(out[out.length - 1]).toBe('new2')
+    expect(out[out.length - 2]).toBe('new1')
+    // 最旧的 'k0' 和 'k1' 被挤出
+    expect(out.includes('k0')).toBe(false)
+    expect(out.includes('k1')).toBe(false)
+  })
+
+  it('empty input', () => {
+    expect(addSeen([], [])).toEqual([])
+    expect(addSeen([], ['a'])).toEqual(['a'])
+    expect(addSeen(['a'], [])).toEqual(['a'])
+  })
+})