feat(发布说明): 新增结构化发布说明组件并更新相关页面

新建 `ReleaseNotes` 结构化发布说明组件，支持按提交类型分组展示并添加对应图标，同时兼容普通Markdown渲染
替换原有 `MarkdownLite` 组件至 `app/launcher/join-beta/page.tsx` 和 `app/download/page.tsx`
更新下载页面的发布说明标题为「此版本的变更」

app/launcher/join-beta/page.tsx

@@ -27,7 +27,7 @@ import {
   Download,
 } from "lucide-react";
 import { cn } from "@/lib/utils";
-import { MarkdownLite } from "@/components/markdown-lite";
+import { ReleaseNotes } from "@/components/release-notes";
 import {
   DOWNLOAD_SOURCES,
   resolveDownloadUrl,
@@ -328,7 +328,7 @@ export default function JoinBetaPage() {
           </h2>
         </div>
         {data.releaseNotes ? (
-          <MarkdownLite text={data.releaseNotes} />
+          <ReleaseNotes text={data.releaseNotes} />
         ) : data.aboutversion ? (
           <>
             <p className="text-muted-foreground leading-relaxed mb-4">