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。

tests/server/checker/engine.test.ts

@@ -19,6 +19,7 @@ function createMockStore(targetNames: string[]) {
         interval_ms: 60000,
         timeout_ms: 5000,
         expect: null,
+        grp: "default",
       }));
     },
     insertCheckResult(result: Record<string, unknown>) {
@@ -32,6 +33,7 @@ function makeCommandTarget(name: string, overrides?: Partial<ResolvedCommandTarg
   return {
     type: "command",
     name,
+    group: "default",
     command: {
       exec: "echo",
       args: ["hello"],
@@ -175,6 +177,7 @@ describe("ProbeEngine", () => {
       const httpTarget: ResolvedHttpTarget = {
         type: "http",
         name: "http-test",
+        group: "default",
         http: {
           url: `http://localhost:${httpServer.port}/`,
           method: "GET",