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/app/infrastructure/data_sources/tushare.py

@@ -14,6 +14,7 @@ from datetime import date, datetime, timedelta
 from decimal import Decimal
 from typing import Any
 
+from app.domain.entities.index import IndexWeight
 from app.domain.entities.market import (
     AdjustFactor,
     DailyBar,
@@ -96,6 +97,28 @@ class TushareProvider:
             for rec in records
         ]
 
+    @staticmethod
+    def normalize_index_weight(
+        records: list[dict[str, Any]], index_code_fallback: str = ""
+    ) -> list[IndexWeight]:
+        """index_weight 接口行 → IndexWeight（index_code/con_code/trade_date/weight）。"""
+        out: list[IndexWeight] = []
+        for rec in records:
+            code = str(rec.get("index_code") or index_code_fallback or "")
+            symbol = str(rec.get("con_code") or "")
+            if not code or not symbol:
+                continue
+            out.append(
+                IndexWeight(
+                    index_code=code,
+                    index_name=rec.get("index_name"),
+                    trade_date=_to_date(rec.get("trade_date")) or date.min,
+                    symbol=symbol,
+                    weight=_to_decimal(rec.get("weight")),
+                )
+            )
+        return out
+
     @staticmethod
     def normalize_daily(records: list[dict[str, Any]]) -> list[DailyBar]:
         bars: list[DailyBar] = []
@@ -224,6 +247,11 @@ class TushareProvider:
 
     _RATE_LIMIT_MARKERS = ("频率超限", "每分钟", "frequenc", "too many")
 
+    def get_index_weight(self, index_code: str) -> list[IndexWeight]:
+        """指数成分（Tushare index_weight 全历史，ts_code 过滤）。"""
+        records = self._call("index_weight", ts_code=index_code)
+        return self.normalize_index_weight(records, index_code_fallback=index_code)
+
     def _call(self, api: str, **kwargs) -> list[dict[str, Any]]:
         """带限速退避的调用：频率超限按指数退避（最长 _rate_limit_wait）等待后重试。"""
         last_error: Exception | None = None