docs: document Tencent quote refresh

src/grid_trading/market/tencent.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import re
 from decimal import Decimal, InvalidOperation
 from typing import Callable, Iterable
+from urllib.error import HTTPError, URLError
 from urllib.request import urlopen
 
 from grid_trading.domain.models import Instrument, QuoteSnapshot
@@ -61,7 +62,10 @@ class TencentQuoteProvider:
             return {}
         query = ",".join(symbols)
         url = f"{self.endpoint}{query}"
-        raw = self._fetcher(url, self.timeout)
+        try:
+            raw = self._fetcher(url, self.timeout)
+        except (OSError, HTTPError, URLError) as exc:
+            raise QuoteFetchError(f"Tencent quote request failed: {exc}") from exc
         return {quote.code: quote for quote in parse_tencent_response(raw)}