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。

scripts/smoke.ts

@@ -12,9 +12,14 @@ await assertExecutableExists(executablePath);
 const tempDir = mkdtempSync(join(tmpdir(), "gc-smoke-"));
 const configPath = join(tempDir, "probes.yaml");
 
+const port = await getFreePort();
+const baseUrl = `http://127.0.0.1:${port}`;
+
 writeFileSync(
   configPath,
-  `targets:
+  `server:
+  port: ${port}
+targets:
   - name: "httpbin"
     type: http
     http:
@@ -25,9 +30,6 @@ writeFileSync(
       status: [200]
 `,
 );
-
-const port = await getFreePort();
-const baseUrl = `http://127.0.0.1:${port}`;
 const app = Bun.spawn([executablePath, configPath], {
   stdout: "pipe",
   stderr: "pipe",