feat(data): B1-2 指数成分同步（Provider + CLI sync index_weight）

- MarketDataProvider.get_index_weight（协议）；Tushare 实现 normalize_index_weight +
  get_index_weight（ts_code=... 全历史成分权重）；Sina 抛 DataSourceNotSupported；
  FailoverProvider 代理并审计每次尝试
- CLI：sync index_weight --code 000300.SH（拉取→幂等落库 index_weight→打印最新快照；
  失败走 sync_log 审计并返回非零）
- tests：Tushare 映射与调用（FakePro）、Failover 主源单源语义（新浪不支持被审计）；
  全量 pytest 通过

backend/tests/test_tushare_provider.py

@@ -224,3 +224,36 @@ class TestGetFinancialWindow:
         assert len(fake.kwargs) == 2
         assert fake.kwargs[1]["end_date"] < fake.kwargs[0]["end_date"]
         assert {r.report_date for r in rows} == {date.fromisoformat(e[:4] + "-" + e[4:6] + "-" + e[6:]) for e in newest + older}
+
+
+class TestIndexWeight:
+    def test_normalize_mapping(self) -> None:
+        from app.infrastructure.data_sources.tushare import TushareProvider
+
+        rows = TushareProvider.normalize_index_weight(
+            [
+                {"index_code": "000300.SH", "con_code": "600519.SH",
+                 "trade_date": "20240628", "weight": 1.53},
+                {"con_code": "000001.SZ", "trade_date": "20240628", "weight": 0.9},
+            ],
+            index_code_fallback="000300.SH",
+        )
+        assert len(rows) == 2
+        assert rows[0].index_code == "000300.SH"
+        assert rows[0].symbol == "600519.SH"
+        assert rows[0].trade_date.isoformat() == "2024-06-28"
+        assert float(rows[0].weight) == 1.53
+        # 无 index_code 时用 fallback；con_code 缺失跳过
+        assert rows[1].index_code == "000300.SH"
+
+    def test_provider_calls_index_weight(self) -> None:
+        from app.infrastructure.data_sources.tushare import TushareProvider
+
+        pro = FakePro(
+            payload=[{"index_code": "000300.SH", "con_code": "600519.SH",
+                      "trade_date": "20240628", "weight": 1.0}]
+        )
+        p = TushareProvider(token="t", pro=pro)
+        rows = p.get_index_weight("000300.SH")
+        assert pro.calls == ["index_weight"]
+        assert len(rows) == 1 and rows[0].symbol == "600519.SH"