fix: 指数K线数据获取

fetch_kline 修复两个bug：
1. _market_prefix 不认识 sh/sz/hk 开头指数代码
2. 指数code自带前缀，API key不要重复拼接
3. fqkline端点同样支持指数，不需要mkline
4. refresh_mtf_cache 加入6大指数自动缓存

上证指数(4163) MA5=4110 MA10=4053 MA20=4070 周线横盘 月线震荡上升

multi_timeframe.py

@@ -57,6 +57,13 @@ def _write_klines_to_db(code: str, daily: list, weekly: list, monthly: list, fun
 def _market_prefix(code: str) -> str:
     """根据代码确定市场前缀"""
     raw = str(code).split("_")[0]
+    # 指数代码：sh/sz/hk开头
+    if raw.startswith("sh"):
+        return "sh"
+    if raw.startswith("sz"):
+        return "sz"
+    if raw.startswith("hk"):
+        return "hk"
     if len(raw) == 5 and raw.isdigit():
         return "hk"
     if raw.startswith("6") or raw.startswith("5"):
@@ -138,8 +145,11 @@ def fetch_kline(code: str, period: str = "day", count: int = 120) -> list:
         return cached_klines
 
     market = _market_prefix(code)
-    url = KLINE_URL.format(market=market, code=code,
-                           period=period, count=count)
+    is_index = any(code.startswith(p) for p in ["sh", "sz", "hk"])
+    
+    # 指数代码已经自带前缀，API直接用code；普通股票需要加market前缀
+    api_code = code if is_index else f"{market}{code}"
+    url = f"http://web.ifzq.gtimg.cn/appstock/app/fqkline/get?param={api_code},{period},,,{count},qfq"
 
     try:
         req = urllib.request.Request(url, headers=_user_agent())
@@ -155,7 +165,10 @@ def fetch_kline(code: str, period: str = "day", count: int = 120) -> list:
     if not isinstance(api_data, dict):
         return {"error": f"data field is {type(api_data).__name__}", "raw": str(api_data)[:200]}
 
-    stock_key = f"{market}{code}"
+    # 指数代码已经自带前缀（sh000001/sz399001），直接用
+    # 普通股票代码需要加market前缀（sh600036/sz300750）
+    is_index = any(code.startswith(p) for p in ["sh", "sz", "hk"])
+    stock_key = code if is_index else f"{market}{code}"
     stock_data = api_data.get(stock_key, {})
 
     # 腾讯API的K线字段名: qfqday, qfqweek, qfqmonth