test(api): couvrir les routes CRUD, random, thèmes et les helpers HTTP

Ajoute les tests des routes /api/cards, /api/cards/[id], /api/cards/random
et /api/cards/themes, ainsi que les tests des helpers http (handleError,
parseJsonBody) et de la factory getCardService. Corrige le formatage des
fichiers sources embarqués non formatés par les commits précédents.

src/app/api/cards/random/route.test.ts

@@ -0,0 +1,53 @@
+// @vitest-environment node
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { NextRequest } from 'next/server'
+import type { Card } from '@/domain/card'
+import { getCardService } from '@/services/card-service-factory'
+import { GET } from './route'
+
+vi.mock('@/services/card-service-factory', () => ({
+  getCardService: vi.fn(),
+}))
+
+const CARD: Card = {
+  id: '10000000-0000-4000-8000-000000000001',
+  question: 'Question ?',
+  response: 'Réponse',
+  theme: 'javascript',
+  tags: ['scope'],
+  createdAt: new Date('2026-01-01T08:00:00Z'),
+  updatedAt: new Date('2026-01-01T08:00:00Z'),
+}
+
+const CARD_JSON = JSON.parse(JSON.stringify(CARD))
+
+describe('GET /api/cards/random', () => {
+  const service = vi.mocked(getCardService)
+
+  beforeEach(() => {
+    service.mockReset()
+  })
+
+  it('tire une carte au hasard sans thème', async () => {
+    const serviceMock = { random: vi.fn().mockResolvedValue(CARD) }
+    service.mockReturnValue(serviceMock as never)
+    const res = await GET(new NextRequest('http://localhost/api/cards/random'))
+    expect(res.status).toBe(200)
+    expect(serviceMock.random).toHaveBeenCalledWith(undefined)
+    expect(await res.json()).toEqual(CARD_JSON)
+  })
+
+  it('tire une carte au hasard pour un thème donné', async () => {
+    const serviceMock = { random: vi.fn().mockResolvedValue(CARD) }
+    service.mockReturnValue(serviceMock as never)
+    const res = await GET(new NextRequest('http://localhost/api/cards/random?theme=javascript'))
+    expect(res.status).toBe(200)
+    expect(serviceMock.random).toHaveBeenCalledWith('javascript')
+  })
+
+  it('propage les erreurs du service', async () => {
+    service.mockReturnValue({ random: vi.fn().mockRejectedValue(new Error('boom')) } as never)
+    const res = await GET(new NextRequest('http://localhost/api/cards/random'))
+    expect(res.status).toBe(500)
+  })
+})