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/app.tsx

@@ -1,14 +1,41 @@
+import { useEffect } from "react";
 import { useSummary } from "./hooks/useSummary";
 import { useTargets } from "./hooks/useTargets";
+import { useTargetDetail } from "./hooks/useTargetDetail";
 import { SummaryCards } from "./components/SummaryCards";
-import { TargetTable } from "./components/TargetTable";
+import { TargetBoard } from "./components/TargetBoard";
+import { TargetDetailModal } from "./components/TargetDetailModal";
 
 export function App() {
   const { data: summary, loading: summaryLoading, error: summaryError } = useSummary();
-  const { data: targets, loading: targetsLoading, error: targetsError } = useTargets();
+  const { data: targets, error: targetsError } = useTargets();
+  const {
+    selectedTarget,
+    trendData,
+    trendLoading,
+    historyData,
+    historyLoading,
+    timeFrom,
+    timeTo,
+    openModal,
+    closeModal,
+    handleTimeChange,
+    handlePageChange,
+  } = useTargetDetail();
 
   const error = summaryError || targetsError;
 
+  useEffect(() => {
+    if (selectedTarget) {
+      document.body.style.overflow = "hidden";
+    } else {
+      document.body.style.overflow = "";
+    }
+    return () => {
+      document.body.style.overflow = "";
+    };
+  }, [selectedTarget]);
+
   return (
     <main className="dashboard">
       <header className="dashboard-header">
@@ -19,7 +46,22 @@ export function App() {
       {error && <div className="error-banner">请求失败: {error}，将在下一次轮询周期自动重试</div>}
 
       <SummaryCards summary={summary} loading={summaryLoading} />
-      <TargetTable targets={targets} loading={targetsLoading} />
+      <TargetBoard targets={targets} onTargetClick={openModal} />
+
+      {selectedTarget && (
+        <TargetDetailModal
+          target={selectedTarget}
+          trendData={trendData}
+          trendLoading={trendLoading}
+          historyData={historyData}
+          historyLoading={historyLoading}
+          timeFrom={timeFrom}
+          timeTo={timeTo}
+          onTimeChange={handleTimeChange}
+          onPageChange={handlePageChange}
+          onClose={closeModal}
+        />
+      )}
     </main>
   );
 }