feat(opensource): README 四级回落 + 兜底 JSON 8 仓 + 项目可见性告警

- site-content.ts：README 取数加 AbortSignal.timeout(10s)（原无超时，
  慢端点可卡整条构建）；四级回落矩阵逐级 console.warn 点名原因：
  新鲜网络（内容有变才回写缓存）→ token 缺位/HTTP 非 2xx/空/超时/异常
  时吃缓存 → 缓存亦缺回落 yaml blurb → 缓存回写失败（构建仓只读）仅告警
- README 图片加固：markdown 层给每个 img 补 loading=lazy + 缺省 alt
  （幂等；只动这两个属性，因为过 rehype-content-sanitize 白名单后其余
  属性会被剥）；相对链接不重写，限制写入 JSDoc 与文档
- projects.ts：单源失败点名、双源全失败点名回落 JSON、mode=only 的
  include 未命中双向点名（双源无此仓 / 被 perSource 过滤掉）
- projects-fallback.json：1 → 8 条真实仓（blog / open-earth-data-guide★58
  / AI-CLI / open-earth-data-kit / pi-mesh / pi-board / pi-jobd /
  ai-code-style-kit，字段对齐 RepoCard）

车道：worker-one（T5）；收编复验：E2E 37/37、构建 48 页 0 ERROR、
兜底 JSON 8 条断言过

验证: E2E 37/37 PASS；pnpm astro build 48 页 exit 0；fallback 8 条

Spec: 2026-11-02_blog-5g-pages (T5)

Co-authored-by: GLM-5.3

src/lib/projects.ts

@@ -74,6 +74,13 @@ export interface LoadProjectsOptions {
 export async function loadProjects(options: LoadProjectsOptions = {}): Promise<RepoCard[]> {
   const { pinned = PINNED_DEFAULT, mode = 'all', include = [], exclude = [], sort = 'pinned-first', perSource = 'both' } = options;
   const [gitea, github] = await Promise.allSettled([fetchJson(GITEA_API), fetchJson(GITHUB_API)]);
+  // 单源失败不拦构建，但必须在日志里点名——否则“怪了，这个仓怎么没显示”要排查很久
+  if (gitea.status === 'rejected') {
+    console.warn(`[opensource] projects：gitea 源不可用（${(gitea.reason as Error).message}），仅用 GitHub 源`);
+  }
+  if (github.status === 'rejected') {
+    console.warn(`[opensource] projects：GitHub 源不可用（${(github.reason as Error).message}），仅用 gitea 源`);
+  }
   const byName = new Map<string, RepoCard>();
 
   for (const r of gitea.status === 'fulfilled' ? gitea.value : []) {
@@ -89,10 +96,42 @@ export async function loadProjects(options: LoadProjectsOptions = {}): Promise<R
   }
 
   if (byName.size === 0) {
+    console.warn('[opensource] projects：双源均无可用数据，改用仓内兜底 src/data/projects-fallback.json');
     const fb = (await import('../data/projects-fallback.json')).default as RepoCard[];
-    return arrange(fb, pinned, mode, include, exclude, sort, perSource);
+    const out = arrange(fb, pinned, mode, include, exclude, sort, perSource);
+    warnMissedIncludes(out, fb, include, mode, perSource);
+    return out;
+  }
+  const merged = [...byName.values()];
+  const out = arrange(merged, pinned, mode, include, exclude, sort, perSource);
+  warnMissedIncludes(out, merged, include, mode, perSource);
+  return out;
+}
+
+/**
+ * mode=only 时点名 include 里“写了却没显示”的仓名——避开设了一个看不见的黑洞。
+ * 未命中分两类，日志措词区分：①双源结果里根本没有（拼写错 / 私有仓 / 该源刚失败）；
+ * ②有，但被 perSource 过滤掉了（配置与仓来源不匹配）。
+ */
+function warnMissedIncludes(
+  showing: RepoCard[],
+  pool: RepoCard[],
+  include: string[],
+  mode: 'all' | 'only' | 'exclude',
+  perSource: 'both' | 'github' | 'gitea',
+): void {
+  if (mode !== 'only' || include.length === 0) return;
+  const shown = new Set(showing.map((r) => r.name));
+  const available = new Map(pool.map((r) => [r.name, r.source]));
+  for (const name of include) {
+    if (shown.has(name)) continue;
+    const src = available.get(name);
+    console.warn(
+      src
+        ? `[opensource] projects：include 里的 「${name}」命中 ${src} 源，但被 perSource=${perSource} 过滤掉——改 perSource=both 或把它移出 include`
+        : `[opensource] projects：include 里的 「${name}」在双源结果中没有命中（仓名拼写？私有仓？源刚失败？）——它不会出现在项目墙上`,
+    );
   }
-  return arrange([...byName.values()], pinned, mode, include, exclude, sort, perSource);
 }
 
 /** 来源过滤 + 可见性过滤 + 排序（不截断：上限交给调用方） */