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/config-loader.test.ts

@@ -479,4 +479,53 @@ targets:
       expect(t.command.env.PATH).toBeDefined();
     }
   });
+
+  test("解析 group 字段", async () => {
+    const configPath = join(tempDir, "group.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "grouped"
+    type: http
+    group: "搜索引擎"
+    http:
+      url: "http://example.com"
+`,
+    );
+
+    const config = await loadConfig(configPath);
+    expect(config.targets[0]!.group).toBe("搜索引擎");
+  });
+
+  test("group 字段默认为 default", async () => {
+    const configPath = join(tempDir, "no-group.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "no-group"
+    type: http
+    http:
+      url: "http://example.com"
+`,
+    );
+
+    const config = await loadConfig(configPath);
+    expect(config.targets[0]!.group).toBe("default");
+  });
+
+  test("非法 group 类型抛出错误", async () => {
+    const configPath = join(tempDir, "bad-group.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "test"
+    type: http
+    group: 123
+    http:
+      url: "http://example.com"
+`,
+    );
+
+    await expect(loadConfig(configPath)).rejects.toThrow("group 字段必须为字符串");
+  });
 });