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/server/checker/config-loader.ts

@@ -100,12 +100,13 @@ function resolveTarget(
 ): ResolvedTarget {
   const intervalMs = parseDuration(target.interval ?? defaults.interval ?? DEFAULT_INTERVAL);
   const timeoutMs = parseDuration(target.timeout ?? defaults.timeout ?? DEFAULT_TIMEOUT);
+  const group = target.group ?? "default";
 
   if (target.type === "http") {
-    return resolveHttpTarget(target, defaults.http, intervalMs, timeoutMs);
+    return resolveHttpTarget(target, defaults.http, intervalMs, timeoutMs, group);
   }
 
-  return resolveCommandTarget(target, defaults.command, intervalMs, timeoutMs, configDir);
+  return resolveCommandTarget(target, defaults.command, intervalMs, timeoutMs, configDir, group);
 }
 
 function resolveHttpTarget(
@@ -113,12 +114,14 @@ function resolveHttpTarget(
   httpDefaults: HttpDefaultsConfig | undefined,
   intervalMs: number,
   timeoutMs: number,
+  group: string,
 ): ResolvedHttpTarget {
   const maxBodyBytes = parseSize(target.http.maxBodyBytes ?? httpDefaults?.maxBodyBytes ?? DEFAULT_MAX_BODY_BYTES);
 
   return {
     type: "http",
     name: target.name,
+    group,
     http: {
       url: target.http.url,
       method: target.http.method ?? httpDefaults?.method ?? DEFAULT_HTTP_METHOD,
@@ -138,6 +141,7 @@ function resolveCommandTarget(
   intervalMs: number,
   timeoutMs: number,
   configDir: string,
+  group: string,
 ): ResolvedCommandTarget {
   const cwd = target.command.cwd ?? commandDefaults?.cwd ?? ".";
   const resolvedCwd = resolve(configDir, cwd);
@@ -151,6 +155,7 @@ function resolveCommandTarget(
   return {
     type: "command",
     name: target.name,
+    group,
     command: {
       exec: target.command.exec,
       args: target.command.args ?? [],
@@ -202,6 +207,11 @@ function validateConfig(config: ProbeConfig): void {
       }
     }
 
+    const group = raw["group"];
+    if (group !== undefined && typeof group !== "string") {
+      throw new Error(`target "${name}" 的 group 字段必须为字符串`);
+    }
+
     if (names.has(name as string)) {
       throw new Error(`target name 重复: "${name}"`);
     }