feat: 重构 Dashboard 为卡片式分组布局

表格布局替换为按分组展示的卡片式布局，新增 group 字段配置和 TargetBoard/TargetCard 等组件。模态框详情页支持时间范围筛选和分页，SummaryCards 减为 3 个。API 端点变更：trend/history 改用 from/to 参数，history 支持分页。recentSampleCount 硬编码为 30。

src/web/components/MiniSparkline.tsx

@@ -0,0 +1,25 @@
+import { Line, LineChart, ResponsiveContainer } from "recharts";
+import type { RecentSample } from "../../shared/api";
+
+interface MiniSparklineProps {
+  data: RecentSample[];
+}
+
+export function MiniSparkline({ data }: MiniSparklineProps) {
+  const chartData = data
+    .filter((s) => s.durationMs !== null)
+    .map((s) => ({ duration: s.durationMs! }))
+    .reverse();
+
+  if (chartData.length === 0) {
+    return <span className="sparkline-empty">-</span>;
+  }
+
+  return (
+    <ResponsiveContainer width={80} height={32}>
+      <LineChart data={chartData}>
+        <Line type="monotone" dataKey="duration" stroke="#356dd2" strokeWidth={1.5} dot={false} />
+      </LineChart>
+    </ResponsiveContainer>
+  );
+}