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, 77 insertions, 0 deletions

diff --git a/frontend/src/lib/dashboardMetrics.test.ts b/frontend/src/lib/dashboardMetrics.test.ts
new file mode 100644
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+++ b/frontend/src/lib/dashboardMetrics.test.ts
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+// @ts-nocheck
+import { describe, expect, it } from 'vitest';
+import { aggregateDashboard, sparkFirstLast } from './dashboardMetrics';
+
+// Leader round2 spec: 登录后默认页顶部一行指标卡——
+// 当前项目数 / 数据集总数 / 运行中-已完成回测数 / AI 用量。
+// 取不到的字段占位 "-"（不得编造数字）。行为合同先定义：
+
+describe('aggregateDashboard', () => {
+  const projects = [{ id: 'p1' }, { id: 'p2' }, { id: 'p3' }];
+  const datasets = [{ id: 'd1' }, { id: 'd2' }];
+  const runs = [
+    { id: 'r1', status: 'running', result: null },
+    { id: 'r2', status: 'queued', result: null },
+    { id: 'r3', status: 'succeeded', result: { metrics: {} } },
+    { id: 'r4', status: 'succeeded', result: { metrics: {} } },
+    { id: 'r5', status: 'failed', result: null }
+  ];
+
+  it('counts projects, datasets and running/done runs from plain item arrays', () => {
+    const x = aggregateDashboard({ projects, datasets, runs, usage: null });
+    expect(x.projectCount).toBe(3);
+    expect(x.datasetCount).toBe(2);
+    expect(x.runningRuns).toBe(2); // queued + running
+    expect(x.doneRuns).toBe(2); // succeeded
+  });
+
+  it('usage label uses real totals when present, "-" placeholder otherwise', () => {
+    const withUsage = aggregateDashboard({
+      projects, datasets, runs,
+      usage: { totals: { input_tokens: 1200, output_tokens: 340, requests: 7 } }
+    });
+    expect(withUsage.usageLabel).toBe('7 次');
+    expect(withUsage.usageTokens).toBe('(1.2k/340 tok)');
+
+    const withoutUsage = aggregateDashboard({ projects, datasets, runs, usage: null });
+    expect(withoutUsage.usageLabel).toBe('-');
+    expect(withoutUsage.usageTokens).toBe('');
+  });
+
+  it('is resilient to missing arrays (fresh account)', () => {
+    const x = aggregateDashboard({ projects: null, datasets: undefined, runs: null, usage: {} });
+    expect(x.projectCount).toBe(0);
+    expect(x.datasetCount).toBe(0);
+    expect(x.runningRuns).toBe(0);
+    expect(x.doneRuns).toBe(0);
+  });
+});
+
+describe('sparkFirstLast (per-project latest backtest equity endpoints)', () => {
+  it('picks the newest run with a result per project and returns first/last equity', () => {
+    const runs = [
+      { id: 'r-old', project_id: 'p1', created_at: '2026-01-01', result: { equity: [
+        { equity: 100 },
+        { equity: 130 } // old run: up
+      ] } },
+      { id: 'r-new', project_id: 'p1', created_at: '2026-02-01', result: { equity: [
+        { equity: 100 },
+        { equity: 90 } // newer run is down — must win over the old run
+      ] } },
+      { id: 'r-broken', project_id: 'p2', created_at: '2026-02-01', result: null },
+      { id: 'r-only', project_id: 'p3', created_at: '2026-02-03', result: { equity: [
+        { equity: 50 },
+        { equity: 50 },
+        { equity: 58 }
+      ] } }
+    ];
+    const m = sparkFirstLast(runs);
+    expect(m.get('p1')).toEqual({ first: 100, last: 90 });
+    expect(m.get('p3')).toEqual({ first: 50, last: 58 });
+    expect(m.has('p2')).toBe(false); // result=null → no sparkline, renders as empty
+  });
+
+  it('returns empty map for no runs', () => {
+    expect([...sparkFirstLast([]).keys()]).toEqual([]);
+  });
+});