feat(sync-history): 新增同步结果查询(每次自动/手动/立即同步的记录)

后端：
- db.py SCHEMA 新增 sync_history 表(不可变,每次同步尝试一行) + 索引
- garmin.py: _log_sync_history() 在 sync_data 全部出口记录; trigger 区分
  auto(调度器)/manual(同步页开始同步)/quick(设置页立即同步); start_sync
  限流拦截分支同样留档; 写入失败只告警不影响同步
- scheduler.py 自动同步传 trigger="auto"; routes 新增 GET /garmin/sync-history
  按时间倒序返回(默认 50 条,上限 200)

前端：
- api.ts 增加 SyncHistoryItem 类型 + getSyncHistory()
- 新页面 /sync-history/ 同步记录: 卡片列表, 状态(成功/失败/被限流)chip 配色,
  时间本地化(今天/昨天/X月X日), 触发类型标签, 范围与耗时
- 同步页与设置页同步区块均加入口链接

backend/tests/test_garmin_sync.py

@@ -845,3 +845,80 @@ class TestSyncWindow:
         assert out["recordsSynced"] == 2, "the days pulled before the 429 are kept"
         assert len([c for c in client.calls if c[0] == "summary"]) == 3
         assert garmin_svc.rate_limited_until(user["id"]) is not None
+
+
+class TestSyncHistory:
+    """Every sync attempt gets one immutable row, whatever its outcome — the
+    record is what lets the 同步记录 screen show what ran, when, and whether
+    it worked. sync_status only keeps the latest state."""
+
+    def test_success_records_one_row(self, db, user):
+        out = garmin_svc.sync_data(user["id"], CREDS, days=1, client=StubClient())
+        assert out["status"] == "success"
+
+        rows = garmin_svc.get_sync_history(user["id"])
+        assert len(rows) == 1
+        row = rows[0]
+        assert row["triggerKind"] == "manual"
+        assert row["status"] == "success"
+        assert row["days"] == 1
+        assert row["recordsSynced"] == 1
+        assert row["startedAt"] and row["finishedAt"]
+        assert row["durationSeconds"] >= 0
+
+    def test_auto_and_quick_triggers_are_tagged(self, db, user):
+        garmin_svc.sync_data(
+            user["id"], CREDS, days=1, client=StubClient(), trigger="auto"
+        )
+        garmin_svc.sync_data(
+            user["id"], CREDS, days=1, client=StubClient(), trigger="quick"
+        )
+        rows = garmin_svc.get_sync_history(user["id"])
+        assert [r["triggerKind"] for r in rows] == ["quick", "auto"], "newest first"
+
+    def test_newest_first(self, db, user):
+        garmin_svc.sync_data(user["id"], CREDS, days=1, client=StubClient())
+        garmin_svc.sync_data(user["id"], CREDS, days=1, client=StubClient())
+        rows = garmin_svc.get_sync_history(user["id"])
+        assert len(rows) == 2
+        assert rows[0]["finishedAt"] >= rows[1]["finishedAt"]
+
+    def test_total_failure_is_recorded(self, db, user):
+        out = garmin_svc.sync_data(
+            user["id"], CREDS, days=2, client=StubClient(fail_days=[day(0), day(1)])
+        )
+        assert out["status"] == "error"
+        assert garmin_svc.get_sync_history(user["id"])[0]["status"] == "error"
+
+    def test_a_429_mid_run_is_recorded(self, db, user):
+        class Throttled(StubClient):
+            def get_user_summary(self, cdate):
+                self.calls.append(("summary", cdate))
+                if cdate == day(1):
+                    raise RuntimeError("too many 429 error responses")
+                return summary()
+
+        garmin_svc.sync_data(user["id"], CREDS, days=2, client=Throttled())
+        assert garmin_svc.get_sync_history(user["id"])[0]["status"] == "rate_limited"
+        garmin_svc._rate_limited_until.clear()
+
+    def test_a_refused_sync_is_still_a_record(self, db, user, monkeypatch):
+        future = datetime.datetime.utcnow() + datetime.timedelta(hours=1)
+        monkeypatch.setitem(garmin_svc._rate_limited_until, user["id"], future)
+
+        out = garmin_svc.sync_data(user["id"], CREDS, days=1, client=StubClient())
+        assert out["status"] == "rate_limited"
+        assert garmin_svc.get_sync_history(user["id"])[0]["status"] == "rate_limited"
+
+    def test_history_is_per_user(self, db, user, make_user):
+        garmin_svc.sync_data(user["id"], CREDS, days=1, client=StubClient())
+        other = make_user("other@example.com")
+        assert garmin_svc.get_sync_history(other["id"]) == []
+
+    def test_history_endpoint_requires_auth(self, client):
+        assert client.get("/api/garmin/sync-history").status_code == 401
+
+    def test_history_endpoint_returns_empty_list(self, client, auth):
+        r = client.get("/api/garmin/sync-history", headers=auth)
+        assert r.status_code == 200
+        assert r.get_json() == {"items": []}