feat(frontend): 首页指标卡与项目行 sparkline（前端重设计第二轮之一）

[变更性质] 新增能力，不动后端。
[新增功能] dashboardMetrics 聚合（项目/数据集/实验/AI 用量统计 + 最近回测首末净值），实盘数据优先、缺数以占位符 '-' 兜底；ProjectMetricRow 渲染 4 张 metric-card；Sparkline 组件输出 up/down 方向线段与端点圆点。
[实现方案] 聚合逻辑与展示组件分离，sparkline 仅依赖 first/last 两个字段，无图表库依赖。
[影响范围] frontend/src/lib 与 components；配套 5 组单测（dashboardMetrics/sparkline/metricRow）。

1 files changed, 66 insertions, 0 deletions

diff --git a/frontend/src/lib/sparkline.test.ts b/frontend/src/lib/sparkline.test.ts
new file mode 100644
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+++ b/frontend/src/lib/sparkline.test.ts
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+// @ts-nocheck
+import { describe, expect, it, vi } from 'vitest';
+import { mount, unmount } from 'svelte';
+import Sparkline from '../components/Sparkline.svelte';
+
+// Leader round2: 项目列表每行内嵌迷你权益缩略图——
+// 用最近一个回测 equity 的首尾点画 sparkline SVG；
+// 无数据就整个组件留空（不渲染 svg）。
+
+describe('Sparkline (real render)', () => {
+  it('renders an svg with a first→last polyline when handed endpoints', async () => {
+    const host = document.createElement('div');
+    const inst = mount(Sparkline, {
+      target: host,
+      props: { first: 100, last: 90, up: false, ariaLabel: '最近回测权益缩略' }
+    });
+    await new Promise((r) => setTimeout(r, 50));
+    const svg = host.querySelector('svg');
+    expect(svg, 'sparkline must be a real svg element').toBeTruthy();
+    const path = svg.querySelector('path, polyline');
+    expect(path).toBeTruthy();
+    const d = (path.getAttribute('d') || path.getAttribute('points')) ?? '';
+    // polyline from left edge to right edge: both endpoints present in geometry
+    expect(d).toContain('0'); // first x
+    const coordsCount = d.trim().split(/[\s,L,M]+/).filter(Boolean).length;
+    expect(coordsCount).toBeGreaterThanOrEqual(4); // 2 points × (x,y)
+    unmount(inst);
+    host.remove();
+  });
+
+  it('renders NOTHING (no svg) for missing data — 留空不渲染', async () => {
+    const host = document.createElement('div');
+    const inst = mount(Sparkline, { target: host, props: { first: null, last: null, ariaLabel: 'x' } });
+    await new Promise((r) => setTimeout(r, 50));
+    expect(host.querySelector('svg')).toBeNull();
+    expect(host.textContent.trim()).toBe('');
+    unmount(inst);
+    host.remove();
+  });
+
+  it('方向语义：down 变红（危险色），up 变绿（成功色）', async () => {
+    const down = document.createElement('div');
+    const inst1 = mount(Sparkline, {
+      target: down,
+      props: { first: 100, last: 90, up: false, ariaLabel: 'x' }
+    });
+    await new Promise((r) => setTimeout(r, 30));
+    const downColor = down.querySelector('path, polyline')?.getAttribute('stroke') ?? '';
+    unmount(inst1);
+    down.remove();
+
+    const up = document.createElement('div');
+    const inst2 = mount(Sparkline, {
+      target: up,
+      props: { first: 100, last: 130, up: true, ariaLabel: 'x' }
+    });
+    await new Promise((r) => setTimeout(r, 30));
+    const upColor = up.querySelector('path, polyline')?.getAttribute('stroke') ?? '';
+    unmount(inst2);
+    up.remove();
+
+    expect(downColor).not.toBe('');
+    expect(upColor).not.toBe('');
+    expect(downColor).not.toBe(upColor);
+  });
+});