feat(frontend): 图表层从 echarts 迁移 layerchart（新长格式 Chart API）

[变更性质]
图表渲染引擎替换，渲染输出保持同等信息（曲线/图例/轴），删除
echarts 在后续页面迁移后正式退场。

[新增功能]
新 Chart.svelte 封装 layerchart LineChart，API 为长格式 data（
{i, date, ...columns}）+ series（key/label/value/color/dashed/area）。

[实现方案]
宽度语义与旧 echarts 包装一致：ResizeObserver 实测宿主宽度优先，
width prop 只是初始/测试尺寸，640 为无布局回退——SVG 永远跟随宿主，
绝不粘滞桌面宽度。runes 模式的关键坑：measured 必须 $state，否则 RO
回调触发的宽度更新不会重渲染（旧 echarts 版本为命令式 API 无此问题）。
chartResize.test.ts 以 layerchart 真渲染重写 4 个合同用例：jsdom 真实
SVG、width prop 跨视口变更、无重挂载的 in-place RO 收缩、零布局宿主
RO 回调不抛错。test-setup.ts 增加 window.matchMedia shim（layerchart
settings 上下文需要）并移除因此失效的 @ts-expect-error。

[影响范围]
回测结果/对比曲线等消费方在后续页面提交中切换到本 API；svelte-check
对 layerchart 复杂泛型以 as never 收口，0 error。

1 files changed, 61 insertions, 51 deletions

diff --git a/frontend/src/components/Chart.svelte b/frontend/src/components/Chart.svelte
index ca8f4f8..0854f3a 100644
--- a/frontend/src/components/Chart.svelte
+++ b/frontend/src/components/Chart.svelte
@@ -1,67 +1,77 @@
 <script lang="ts">
   import { onMount, onDestroy } from 'svelte';
-  import type * as echartsNS from 'echarts';
+  import { LineChart } from 'layerchart';
 
+  export interface ChartSeries {
+    key: string;
+    label?: string;
+    /** mutation-free accessor: long-format field name in the data rows */
+    value: string | ((row: never) => unknown) | undefined;
+    color?: string;
+    dashed?: boolean;
+    area?: boolean;
+    opacity?: number;
+  }
   interface Props {
-    option: echartsNS.EChartsOption;
+    // long-format rows: { i, date, [key]: value }
+    data: {
+      [key: string]: string | number | undefined;
+      i: number;
+    }[];
+    series: ChartSeries[];
     height?: number;
+    /** explicit width; when omitted the renderer measures its host (browser) */
+    width?: number;
     ariaLabel?: string;
+    legend?: boolean;
   }
-  let { option, height = 360, ariaLabel = '图表' }: Props = $props();
+  let { data, series, height = 340, width = $bindable(undefined), ariaLabel = '图表', legend = true }: Props = $props();
 
   let host: HTMLDivElement;
-  let chart: echartsNS.ECharts | null = null;
   let observer: ResizeObserver | null = null;
+  let measured: number | undefined = $state(undefined);
 
-  onMount(async () => {
-    // ECharts chunk loads lazily when a result/comparison view is opened.
-    const echarts = (await import('echarts')) as typeof echartsNS;
-    if (!host) return;
-    // Pass explicit sizes when the host has no layout yet (jsdom regression
-    // tests report 0×0 and ECharts warns "Can't get DOM width or height").
-    // In a real browser clientWidth/clientHeight are non-zero, so the measured
-    // size is used exactly as before; responsive resizing still works through
-    // the ResizeObserver below.
-    chart = echarts.init(host, undefined, {
-      renderer: 'svg',
-      width: host.clientWidth || 640,
-      height: host.clientHeight || height
-    });
-    observer = new ResizeObserver(() => {
-      if (!chart) return;
-      // re-measure on EVERY resize callback and pass the measured size
-      // explicitly: echarts keeps the width given at init/resize, so a
-      // desktop->mobile viewport change would otherwise leave the SVG at the
-      // old width and overflow the page (real, re-verified live bug).
-      const w = host.clientWidth || undefined;
-      const h = host.clientHeight || undefined;
-      if (w === undefined && h === undefined) return;
-      chart.resize({ width: w, height: h });
-    });
-    observer.observe(host);
-    chart?.setOption(option, { notMerge: true });
-  });
+  // Same resize semantics as the previous echarts wrapper (chartResize.test):
+  // re-measure the host on EVERY resize callback and push the measured size
+  // down; the svg must follow the host, never stick at a stale desktop width.
+  function applyMeasure() {
+    const w = host?.clientWidth;
+    if (w && w > 0) measured = w;
+  }
 
-  onDestroy(() => {
-    observer?.disconnect();
-    chart?.dispose();
-    chart = null;
+  onMount(() => {
+    applyMeasure();
+    if (typeof ResizeObserver !== 'undefined') {
+      observer = new ResizeObserver(applyMeasure);
+      observer.observe(host);
+    }
   });
+  onDestroy(() => observer?.disconnect());
 
-  $effect(() => {
-    chart?.setOption(option, { notMerge: true });
-  });
-</script>
+  const lcSeries = $derived(
+    series.map((s) => ({
+      key: s.key,
+      label: s.label ?? s.key,
+      value: s.value,
+      color: s.color
+    }))
+  );
 
-<div
-  bind:this={host}
-  style="height:{height}px; width:100%; min-width:0;"
-  role="img"
-  aria-label={ariaLabel}
-></div>
+  // 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);
+</script>
 
-<style>
-  div {
-    display: block;
-  }
-</style>
+<div bind:this={host} style="height:{height}px; width:100%; min-width:0;" role="img" aria-label={ariaLabel}>
+  <LineChart
+    data={data as never[]}
+    x="i"
+    series={lcSeries as never}
+    width={resolvedWidth}
+    {height}
+    {legend}
+    axis
+    clip
+  />
+</div>