持仓排名数据清洗，机构名称为空时用名次兜底

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ft-app/app/collector.py

@@ -293,10 +293,14 @@ def fetch_position_rankings(contract_code: str, trade_date: str) -> list[dict]:
 
         for _, row in df.iterrows():
             try:
+                inst = str(row["会员简称"]).strip()
+                rank = int(row["名次"])
+                if inst in ("-", ""):
+                    inst = f"-{rank}"
                 results.append({
                     "data_type": dtype,
-                    "rank": int(row["名次"]),
+                    "rank": rank,
-                    "institution": str(row["会员简称"]),
+                    "institution": inst,
                     "value": int(row.iloc[2]),
                     "change": int(row["比上交易增减"]),
                 })