feat(cms): 首页四项可配 + 开源页项目可见性 + GitHub README 开篇

- 首页：subtitle（markdown 短文本）｜latestPhotos 0-6（0 隐藏）｜
  perTrackLimit 4-8｜sections{tracks,photos,heatmap,projects} 开关，
  访问器 homeConfig() 夹取越界值，字段级回落默认（零配置=原形态）
- 开源页项目可见性：mode all|only|exclude + include[]/exclude[] +
  sort pinned-first|stars|updated + perSource both|github|gitea；
  projects.ts 加 LoadProjectsOptions + arrange()（来源→可见性→排序）
- 开源页开篇支持 GitHub README：intro_from off|github-readme，构建期
  取 wait4xx/wait4xx README（token 复用宿主 0600 文件）→ 缓存
  content/.github-readme.md 入仓 → renderMarkdown；失败逐级回落
  （缓存 → yaml blurb）。实测取到 3117 字符，现状仍 off 待用户开启
- 修既有 bug：orderPinned 内硬 slice(0,6) 把开源页 limit=99 也截到 6 条
  → 移除，开源页恢复全量 16 条
- 文档：写作指南加首页/项目墙两张字段表（含 YAML 1.1 `off` 需加引号坑、
  README 行为与外部徽章风险说明）

车道：op-gitea（3/3）；收编复验：构建 48 页 + E2E 37/37 + 开源页 16 条 +
首页默认形态（2 轨/热力图/项目墙）无回归

验证: node v26.13.0 构建 48 页 exit 0；E2E 37/37 PASS；playwright 实测

Spec: none (首页与开源页后台扩展，车道级交付)

Co-authored-by: GLM-5.3

src/pages/index.astro

@@ -8,14 +8,17 @@ import ProjectWall from '../components/geek/ProjectWall.astro';
 import Heatmap from '../components/geek/Heatmap.astro';
 import { fetchHeartbeat, agoZh } from '../lib/heartbeat';
 import { t } from '../i18n/ui';
-import { homeTagline } from '../lib/site-content';
+import { homeConfig, homeTagline, renderMarkdown } from '../lib/site-content';
 import SocialLinks from '../components/SocialLinks.astro';
 
+// 首页可配项（后台主页设置）：副标题/影像张数/区块开关/每轨条数，字段级回落
+const cfg = await homeConfig('zh');
+const subtitleHtml = cfg.subtitle ? await renderMarkdown(cfg.subtitle) : '';
 const posts = (await getCollection('posts', ({ data }) => !data.draft && !data.tags.includes('hidden'))).sort(
   (a, b) => b.data.pubDate.getTime() - a.data.pubDate.getTime(),
 );
 // 最新影像取集合前 4 张；照片时间序由照片管线（exif 车道）治理，此处只裁切
-const photos = (await getCollection('photos')).slice(0, 4);
+const photos = (await getCollection('photos')).slice(0, Math.max(1, cfg.latestPhotos));
 const heartbeat = await fetchHeartbeat();
 // 身份语改由 content/site/home.yaml 供给（后台可改），缺值回落默认文案
 const tagline = await homeTagline('zh');
@@ -24,11 +27,13 @@ const tagline = await homeTagline('zh');
 <BaseLayout title="wait4x">
   <IdCard>
         <p class="tagline">{tagline}</p>
+    {subtitleHtml && <div class="subtitle" set:html={subtitleHtml} />}
 <SocialLinks />
     </IdCard>
 
-  <PostList {posts} perTrack={6} />
+  {cfg.sections.tracks && <PostList {posts} perTrack={cfg.perTrackLimit} />}
 
+  {cfg.sections.photos && cfg.latestPhotos > 0 && (
   <section class="latest" aria-label="最新影像">
     <div class="latest-head">
       <span class="lab">最新影像</span>
@@ -50,8 +55,9 @@ const tagline = await homeTagline('zh');
       ))}
     </div>
   </section>
+  )}
 
-  <Heatmap
+  {cfg.sections.heatmap && <Heatmap
     labels={{
       title: t('heatmap_title', 'zh'),
       summary: t('heatmap_summary', 'zh'),
@@ -59,8 +65,8 @@ const tagline = await homeTagline('zh');
       more: t('heatmap_more', 'zh'),
       note: t('heatmap_note', 'zh'),
     }}
-  />
-  <ProjectWall />
+  />}
+  {cfg.sections.projects && <ProjectWall />}
   {heartbeat && (
     <p class="heartbeat" aria-label="最近心跳">
       <span class="beat-dot" aria-hidden="true"></span>
@@ -70,6 +76,14 @@ const tagline = await homeTagline('zh');
 </BaseLayout>
 
 <style>
+  .subtitle {
+    font-size: 13.5px;
+    color: var(--ink-4);
+    margin-top: 2px;
+    letter-spacing: 0.01em;
+  }
+  .subtitle :global(p) { margin: 0; }
+  .subtitle :global(a) { color: var(--accent); }
   .tagline {
     font-size: 14px;
     color: var(--ink-3);