feat: 메인 현재 시각을 최근 통신 기준으로 갱신

완료 턴 시각 대신 lobby serverTime을 분 경계에 맞춰 표시한다. 게임 API 응답과 SSE 및 같은 계정 탭 전달을 최근 통신으로 기록하고, 45초 공백에는 시계를 멈춘다. 공통 시계 투영과 단위 및 Chromium 회귀 검증을 추가한다.

app/game-frontend/test/serverClockProjection.test.ts

@@ -0,0 +1,51 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import {
+    millisecondsUntilNextMinute,
+    projectServerClock,
+    sampleServerClock,
+} from '../src/utils/serverClockProjection.ts';
+
+void test('projects a running server clock from the browser sample instant', () => {
+    const sample = sampleServerClock(
+        {
+            serverTime: '2026-08-13T00:00:35.250Z',
+            clockMode: 'realtime',
+            clockRunning: true,
+        },
+        10_000
+    );
+    assert.ok(sample);
+    assert.equal(projectServerClock(sample, 34_750).time.toISOString(), '2026-08-13T00:01:00.000Z');
+    assert.equal(millisecondsUntilNextMinute(projectServerClock(sample, 10_000).time), 24_750);
+});
+
+void test('keeps manual clocks fixed even while client time advances', () => {
+    const sample = sampleServerClock(
+        { serverTime: '2026-08-13T00:00:35.000Z', clockMode: 'manual', clockRunning: false },
+        10_000
+    );
+    assert.ok(sample);
+    assert.equal(projectServerClock(sample, 130_000).time.toISOString(), '2026-08-13T00:00:35.000Z');
+});
+
+void test('holds a preopen clock until its wall-clock start delay passes', () => {
+    const sample = sampleServerClock(
+        {
+            serverTime: '2026-08-13T00:00:00.000Z',
+            serverWallTime: '2026-08-13T08:00:00.000Z',
+            clockMode: 'realtime',
+            clockRunning: false,
+            clockStartsAt: '2026-08-13T08:01:00.000Z',
+        },
+        10_000
+    );
+    assert.ok(sample);
+    assert.equal(projectServerClock(sample, 69_999).time.toISOString(), '2026-08-13T00:00:00.000Z');
+    assert.equal(projectServerClock(sample, 70_001).time.toISOString(), '2026-08-13T00:00:00.001Z');
+});
+
+void test('rejects an invalid server clock sample', () => {
+    assert.equal(sampleServerClock({ serverTime: 'not-a-time' }, 10_000), null);
+});