feat(frontend): 图表增强——网格、hover 当日净值/回撤、回测区间阴影带

[变更性质] 图表层能力扩展，前端重设计第二轮之三。
[新增功能] Chart 网格线使用主题 border 色；hover 手柄提示补充"当日净值+回撤"；回测区间 belowMarks 渲染半透明阴影带（bandShaded 可关）；series 支持 dashed/opacity，Area 填充渲染；equity 行内合并回撤列，drawdown 图改为百分比格式化。
[实现方案] 基于 layerchart marks/belowMarks 泳道与自定义 tooltip snippet（lcExtras 透传绕开字面量类型检查），宽度扩展点保持 resolvedWidth 合同不变。
[影响范围] Chart.svelte、ProjectResultsTab.svelte；图表 probe 断言（svgs 渲染、溢出为 0）不变。

2 files changed, 138 insertions, 19 deletions

diff --git a/frontend/src/components/Chart.svelte b/frontend/src/components/Chart.svelte
index 0854f3a..5b6038d 100644
--- a/frontend/src/components/Chart.svelte
+++ b/frontend/src/components/Chart.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { onMount, onDestroy } from 'svelte';
-  import { LineChart } from 'layerchart';
+  import { LineChart, Spline, Area, Tooltip } from 'layerchart';
+  import type { ChartState, Facet } from 'layerchart';
 
   export interface ChartSeries {
     key: string;
@@ -12,6 +13,12 @@
     area?: boolean;
     opacity?: number;
   }
+  /** hover 提示里追加的"非曲线"行（如权益曲线上的当日回撤） */
+  interface TooltipExtra {
+    key: string;
+    label: string;
+    color?: string;
+  }
   interface Props {
     // long-format rows: { i, date, [key]: value }
     data: {
@@ -24,8 +31,28 @@
     width?: number;
     ariaLabel?: string;
     legend?: boolean;
+    /** 回测区间页面阴影（浅色高亮带；默认开） */
+    bandShaded?: boolean;
+    /** 悬浮数值（在曲线序列之外）追加的行 */
+    extras?: TooltipExtra[];
+    valueFormatter?: (v: string | number | undefined) => string;
   }
-  let { data, series, height = 340, width = $bindable(undefined), ariaLabel = '图表', legend = true }: Props = $props();
+  let {
+    data,
+    series,
+    height = 340,
+    width = $bindable(undefined),
+    ariaLabel = '图表',
+    legend = true,
+    bandShaded = true,
+    extras = [],
+    valueFormatter = (v) =>
+      v === undefined || v === null
+        ? '—'
+        : typeof v === 'number'
+          ? v.toLocaleString('zh-Hans', { maximumFractionDigits: 4 })
+          : String(v)
+  }: Props = $props();
 
   let host: HTMLDivElement;
   let observer: ResizeObserver | null = null;
@@ -48,22 +75,103 @@
   });
   onDestroy(() => observer?.disconnect());
 
+  // series config for layerchart: dashed/opacity 走本 series 的 props，
+  // Spline 会合并 ctx.series?.props（含 highlight Points）。
   const lcSeries = $derived(
-    series.map((s) => ({
-      key: s.key,
-      label: s.label ?? s.key,
-      value: s.value,
-      color: s.color
-    }))
+    series.map((s) => {
+      const branchStyle: Record<string, unknown> = s.dashed
+        ? { strokeDasharray: '6 6', opacity: s.opacity ?? 0.65 }
+        : s.opacity !== undefined
+          ? { opacity: s.opacity }
+          : {};
+      const cfg: Record<string, unknown> = {
+        key: s.key,
+        label: s.label ?? s.key,
+        value: s.value,
+        color: s.color
+      };
+      if (s.dashed || s.opacity !== undefined) cfg.props = branchStyle;
+      return cfg;
+    })
   );
 
+  // key → 画面积填充（回撤曲线 area 语义）
+  const areaKeys = $derived(new Set(series.filter((s) => s.area).map((s) => s.key)));
+
+  // LineChartProps 未声明 tooltip（自定义片段经 restProps 链传给 ChartChildren），
+  // 用展开绕开精确字面量检查。
+  const lcExtras = $derived({ tooltip: tooltipBox });
+
   // Resize semantics (chartResize.test contract): a live host measurement
   // always wins (the svg follows the real viewport), the width prop is the
   // initial/testing size, 640 is the no-layout fallback.
   const resolvedWidth = $derived(measured ?? width ?? 640);
+
+  type ChartCtx = ChartState<any, any, any>;
+
+  /**
+   * 回测区间阴影带的坐标（belowMarks：网格之上、曲线之下）。取
+   * xScale/yScale 的 range：即 padding 后的绘图区矩形。
+   */
+  function bandBounds(context: ChartCtx | undefined): { x: number; y: number; w: number; h: number } | null {
+    const xr: number[] | undefined = context?.xScale?.range?.() as number[] | undefined;
+    const yr: number[] | undefined = context?.yScale?.range?.() as number[] | undefined;
+    if (context === undefined || xr === undefined || yr === undefined) return null;
+    const w = xr[1] - xr[0];
+    if (w <= 0) return null;
+    const y = Math.min(yr[0], yr[1]);
+    const h = Math.abs(yr[1] - yr[0]);
+    return { x: xr[0], y, w, h };
+  }
 </script>
 
-<div bind:this={host} style="height:{height}px; width:100%; min-width:0;" role="img" aria-label={ariaLabel}>
+{#snippet belowMarks({ context }: { context: ChartCtx; facet: Facet })}
+  {#if bandShaded}
+    {@const b = bandBounds(context)}
+    {#if b}
+      <rect
+        x={b.x}
+        y={b.y}
+        width={b.w}
+        height={b.h}
+        fill="var(--chart-band, rgba(15, 118, 110, 0.05))"
+      />
+    {/if}
+  {/if}
+{/snippet}
+
+{#snippet marks({ context }: { context: ChartCtx; facet: Facet })}
+  {#each context?.series?.visibleSeries ?? [] as s (s.key)}
+    {#if areaKeys.has(s.key)}
+      <Area seriesKey={s.key} opacity={0.9} fill="var(--chart-area-fill, rgba(15, 118, 110, 0.12))" />
+    {/if}
+    <Spline seriesKey={s.key} stroke-width={2} />
+  {/each}
+{/snippet}
+
+{#snippet tooltipBox({ context }: { context: ChartCtx })}
+  <Tooltip.Root>
+    {#snippet children({ data }: { data: Record<string, string | number | undefined> })}
+      <Tooltip.Header value={data?.date ?? ''} />
+      <Tooltip.List>
+        {#each context?.series?.visibleSeries ?? [] as s (s.key)}
+          {@const acc = s?.value}
+          {@const v = typeof acc === 'function' ? acc(data as never) : data?.[acc as string]}
+          {#if v !== undefined}
+            <Tooltip.Item label={s.label} value={v} color={s.color} format={valueFormatter} valueAlign="right" />
+          {/if}
+        {/each}
+        {#each extras as e (e.key)}
+          {#if data?.[e.key] !== undefined}
+            <Tooltip.Item label={e.label} value={data?.[e.key]} color={e.color} format={valueFormatter} valueAlign="right" />
+          {/if}
+        {/each}
+      </Tooltip.List>
+    {/snippet}
+  </Tooltip.Root>
+{/snippet}
+
+<div bind:this={host} style="height:{height}px; width:100%; min-width:0;" role="img" aria-label={ariaLabel} data-testid="chart-host">
   <LineChart
     data={data as never[]}
     x="i"
@@ -73,5 +181,10 @@
     {legend}
     axis
     clip
+    props={{ grid: { stroke: 'var(--border)' }, spline: { 'stroke-width': 2 } }}
+    highlight={{ lines: true, points: true }}
+    {belowMarks}
+    {marks}
+    {...lcExtras}
   />
 </div>
diff --git a/frontend/src/pages/ProjectResultsTab.svelte b/frontend/src/pages/ProjectResultsTab.svelte
index 5ff03c0..f479116 100644
--- a/frontend/src/pages/ProjectResultsTab.svelte
+++ b/frontend/src/pages/ProjectResultsTab.svelte
@@ -55,16 +55,22 @@
   const result = $derived<BacktestResult | null>(run?.result ?? null);
   const hasEquity = $derived(!!result && result.equity.length > 0);
 
-  // long-format rows for the layerchart renderer ({ i, date, ...columns })
+  // long-format rows for the layerchart renderer ({ i, date, ...columns });
+  // equity rows同时携带 dd（当日回撤%），供 hover 提示读数
   const equityData = $derived.by(() => {
     if (!result || !hasEquity) return [];
-    return result.equity.map((p, i) => ({
-      i,
-      date: p.date,
-      equity: p.equity,
-      cash: p.cash,
-      benchmark: p.benchmark ?? undefined
-    }));
+    let peak = -Infinity;
+    return result.equity.map((p, i) => {
+      peak = Math.max(peak, p.equity);
+      return {
+        i,
+        date: p.date,
+        equity: p.equity,
+        cash: p.cash,
+        benchmark: p.benchmark ?? undefined,
+        dd: peak <= 0 ? 0 : -((peak - p.equity) / peak) * 100
+      };
+    });
   });
 
   const hasBench = $derived(equityData.some((r) => r.benchmark !== undefined && r.benchmark !== null));
@@ -193,9 +199,9 @@
           <Button variant={chartMode === "drawdown" ? "default" : "outline"} size="sm" aria-pressed={chartMode === "drawdown"} onclick={() => (chartMode = "drawdown")}>回撤曲线</Button>
         </div>
         {#if chartMode === "equity"}
-          <Chart data={equityData} series={equitySeries} ariaLabel="策略权益曲线" height={340} />
+          <Chart data={equityData} series={equitySeries} ariaLabel="策略权益曲线" height={340} extras={[{ key: 'dd', label: '回撤', color: '#134e4a' }]} />
         {:else}
-          <Chart data={drawdownData} series={drawdownSeries} ariaLabel="回撤曲线" height={300} />
+          <Chart data={drawdownData} series={drawdownSeries} ariaLabel="回撤曲线" height={300} valueFormatter={(v) => (typeof v === 'number' ? `${v.toFixed(2)}%` : String(v))} />
         {/if}
       </div>