feat(board): expose summarize_by_machine for offload visibility (A-1)

요약 풀의 머신별 완료 실적(맥미니 vs 맥북)을 /api/queue/overview 응답에
summarize_by_machine 로 노출. rows_to_summarize_split 이 이미 계산하던 값의
additive 투영 — 신규 수집 SQL/마이그 0. 통합 보드 레인의 오프로드 가시화
(맥북이 요약 86% 처리) 재료. + FE 타입 동기 + store 신선도 timestamp(B-4).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_queue_overview.py

@@ -103,6 +103,32 @@ def test_summarize_pool_split_attribution():
     assert macbook["pending"] == 0              # 풀 pending 은 macmini 만
 
 
+def test_summarize_by_machine_projection():
+    """build_summarize_by_machine = split 의 done_1h/done_today 를 머신별로 투영
+    (done_15m 은 제외 — 내부 state 판정 전용)."""
+    from services.queue_overview import build_summarize_by_machine
+    split = _split(
+        macbook={"done_1h": 226, "done_today": 312, "done_15m": 60},
+        macmini={"done_1h": 37, "done_today": 94, "done_15m": 9},
+    )
+    sbm = build_summarize_by_machine(split)
+    assert sbm == {
+        "macmini": {"done_1h": 37, "done_today": 94},
+        "macbook": {"done_1h": 226, "done_today": 312},
+    }
+    assert "done_15m" not in sbm["macbook"]
+
+
+def test_compose_overview_includes_summarize_by_machine():
+    """compose_overview 응답 계약에 summarize_by_machine 포함 (FE 레인 분담 재료)."""
+    now_kst = datetime(2026, 6, 13, 13, 0, tzinfo=KST)
+    stats = {"summarize": _stage(pending=1317, done_1h=264)}
+    split = _split(macbook={"done_1h": 226, "done_today": 312}, macmini={"done_1h": 37, "done_today": 94})
+    ov = compose_overview(stats, split, {}, {}, [], deep_enabled=True, now_kst=now_kst)
+    assert ov["summarize_by_machine"]["macbook"]["done_1h"] == 226
+    assert ov["summarize_by_machine"]["macmini"]["done_today"] == 94
+
+
 def test_deep_disabled_deep_summary_counts_to_macmini():
     stats = {"deep_summary": _stage(pending=2, processing=1, done_1h=3, done_today=4)}
     machines = build_machines(stats, _split(), [], deep_enabled=False)