fix(HEL-494): 日K默认45根并修复问天行业0/205覆盖

悬浮窗和详情页只画最近45个交易日，中枢仍保留250日历史。盘后缺sw_daily时保留成分日线内核，外显走免费申万；成分行情改为全市场快照+分页，不再截成前60只。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

frontend/pages/market/preview.js

@@ -368,10 +368,7 @@ function selectStockPreviewChart(chart) {
   } else if ((payload.prices || []).length) {
     setText("stockPreviewDate", payload.meta?.trade_date || "最新行情");
     const notice = String(payload.meta?.notice || "").trim();
-    setText(
-      "stockPreviewSource",
-      notice ? `日 K 行情 · ${payload.prices.length} 个交易日 · ${notice}` : `日 K 行情 · ${payload.prices.length} 个交易日`,
-    );
+    setText("stockPreviewSource", dailyChartSourceLabel(payload.prices, notice));
     drawDailyPreviewChart(payload.prices);
   } else {
     setText("stockPreviewDate", payload.meta?.trade_date || "最新行情");