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/data/projects-fallback.json

@@ -7,5 +7,68 @@
     "stars": 0,
     "url": "https://git.wait4x.online/wait4x/blog",
     "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "open-earth-data-guide",
+    "description": "A one-stop index of public earth-system (meteo · ocean · climate · environment) data sources — download channels & access notes. Companion CLI toolkit: open-earth-data-kit.",
+    "language": "Python",
+    "stars": 58,
+    "url": "https://github.com/wait4xx/open-earth-data-guide",
+    "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "AI-CLI",
+    "description": "Run Terminal or AI coding assistants (Claude Code, Aider, etc.) on your phone/tablet — a responsive web IDE with terminal, split-pane editor, file browser, and real-time collaboration",
+    "language": "TypeScript",
+    "stars": 2,
+    "url": "https://github.com/wait4xx/AI-CLI",
+    "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "open-earth-data-kit",
+    "description": "Unified CLI toolkit for public meteorological, oceanographic, climate and environmental data access.",
+    "language": "Python",
+    "stars": 2,
+    "url": "https://github.com/wait4xx/open-earth-data-kit",
+    "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "pi-mesh",
+    "description": "Live agent-to-agent communication for Pi — local broker, mesh.v1 protocol, honest delivered/read/answered statuses, hash-only ledger. Zero runtime deps.",
+    "language": "TypeScript",
+    "stars": 0,
+    "url": "https://github.com/wait4xx/pi-mesh",
+    "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "pi-board",
+    "description": "Shared context board for pi-mesh — typed entries, bounded store, boolean grep. CLI-first; the mesh stays the router, never the database.",
+    "language": "TypeScript",
+    "stars": 1,
+    "url": "https://github.com/wait4xx/pi-board",
+    "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "pi-jobd",
+    "description": "Detached local job runner for Pi — per-user daemon, honest statuses, crash adoption, cross-platform. Zero runtime dependencies.",
+    "language": null,
+    "stars": 0,
+    "url": "https://github.com/wait4xx/pi-jobd",
+    "updatedAt": ""
+  },
+  {
+    "source": "github",
+    "name": "ai-code-style-kit",
+    "description": "Comment & commit-message style kit for AI-assisted coding: cross-tool skills, cross-platform git hook, pi extension",
+    "language": "Shell",
+    "stars": 0,
+    "url": "https://github.com/wait4xx/ai-code-style-kit",
+    "updatedAt": ""
   }
 ]