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/shared/api.ts

@@ -15,26 +15,37 @@ export interface SummaryResponse {
   total: number;
   up: number;
   down: number;
-  avgDurationMs: number | null;
   lastCheckTime: string | null;
 }
 
+export interface RecentSample {
+  timestamp: string;
+  durationMs: number | null;
+  up: boolean;
+}
+
 export interface TargetStatus {
   id: number;
   name: string;
   type: string;
   target: string;
+  group: string;
   interval: string;
   latestCheck: CheckResult | null;
   stats: TargetStats;
-  sparkline: number[];
+  recentSamples: RecentSample[];
 }
 
 export interface TargetStats {
   totalChecks: number;
   availability: number;
-  avgDurationMs: number | null;
-  p99DurationMs: number | null;
+}
+
+export interface HistoryResponse {
+  items: CheckResult[];
+  total: number;
+  page: number;
+  pageSize: number;
 }
 
 export interface CheckResult {