feat(web): K线图库对比 —— TradingView Lightweight Charts 实现 + 双库切换

- 按确认方案「两套实现并存对比」：
  - npm 依赖 lightweight-charts@4.2.3（v3 §21 推荐库）
  - components/StockChart/chartTypes.ts：共享 props 接口
  - CandleChart.tsx（ECharts 版，重构复用共享类型）+ CandleChartLW.tsx
    （Lightweight 版：蜡烛+成交量副刻度+MA+成交实心箭头/未成交信号圆点 markers）
  - StockChart.tsx wrapper；个股页顶部「ECharts / Lightweight」切换（默认 Lightweight）
- /stocks/600519.SH 冒烟 200；tsc --noEmit 通过

frontend/web/app/stocks/[symbol]/page.tsx

@@ -18,7 +18,8 @@ import {
   Empty,
   SkeletonLines,
 } from "@/components/ui";
-import { CandleChart, type CandleDatum } from "@/components/StockChart/CandleChart";
+import type { CandleDatum } from "@/components/StockChart/chartTypes";
+import { StockChart, type ChartLibrary } from "@/components/StockChart/StockChart";
 
 export default function StockResearchPage() {
   const params = useParams<{ symbol: string }>();
@@ -28,6 +29,7 @@ export default function StockResearchPage() {
   const [signalMarkers, setSignalMarkers] = useState<ChartMarker[]>([]);
   const [selectionMarkers, setSelectionMarkers] = useState<ChartMarker[]>([]);
   const [adjust, setAdjust] = useState<"none" | "qfq" | "hfq">("none");
+  const [chartLib, setChartLib] = useState<ChartLibrary>("lightweight");
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState("");
 
@@ -80,6 +82,11 @@ export default function StockResearchPage() {
         }
         actions={
           <div className="row" style={{ gap: 6 }}>
+            {(["echarts", "lightweight"] as const).map((l) => (
+              <Btn key={l} variant={chartLib === l ? "primary" : undefined} onClick={() => setChartLib(l)}>
+                {l === "echarts" ? "ECharts" : "Lightweight"}
+              </Btn>
+            ))}
             {(["none", "qfq", "hfq"] as const).map((m) => (
               <Btn
                 key={m}
@@ -113,7 +120,8 @@ export default function StockResearchPage() {
             {candles.length === 0 ? (
               <Empty icon="chartLine" title="无 K 线数据" hint="该区间/口径没有行情（可能停牌或未同步）。" />
             ) : (
-              <CandleChart
+              <StockChart
+                library={chartLib}
                 data={candles}
                 volume={chart?.volume ?? []}
                 indicators={chart?.indicators ?? {}}