fix(frontend): restore phase-gating build

frontend/tests/vertical-slice.test.ts

@@ -56,7 +56,15 @@ function makeApiMock(overrides?: Partial<ApiClient>): ApiClient {
         session: { code: 'ABCD12', status: 'lie', current_round: 1 },
         round: { number: 1, category: { slug: 'history', name: 'History' } }
       }
-    })
+    }),
+    showQuestion: vi.fn(),
+    mixAnswers: vi.fn(),
+    calculateScores: vi.fn(),
+    getScoreboard: vi.fn(),
+    startNextRound: vi.fn(),
+    finishGame: vi.fn(),
+    submitLie: vi.fn(),
+    submitGuess: vi.fn()
   };
 
   return { ...base, ...overrides };