feat(art): replace all 72 posts' artwork with the v2 pipeline

Every post now carries one unique local-ComfyUI/Ideogram 4 base frame, composited
into EN + ZH share cards, a banner and list thumbs.

- the shipped prompts_catalog held only 21 distinct metaphors for 72 posts (16
  shared one visual), so all 72 were rewritten as unique object+state metaphors
  and 10 frames re-rolled after OCR found pseudo-text rendered at legible size
- render_from_art.mjs emits JPEG by default (558 KB PNG -> 84 KB mozjpeg q85);
  the ZH 1200x630 card did not exist before this batch
- 288 frontmatter fields migrated; the 144 v1 PNGs are gone
- PostList's thumb helper keys off the base slug (a ZH card is zh-<slug>.jpg while
  the thumb is <slug>-800.webp, which 404'd the whole ZH listing)
- [...slug].astro's <picture> regex accepts .jpg
- the repo now carries the art inputs (metaphors.json, captions/<slug>.json,
  refreshed prompts_catalog.json) so a frame is reproducible from git alone

src/content/posts/zh/syncing-a-self-improving-ai-agent-across-machines.md

@@ -5,8 +5,8 @@ pubDate: 2026-02-18
 updatedDate: 2026-09-11
 category: case-studies
 tags: [hermes, git, gitea, ai-agents, devops, sync]
-ogImage: /og/syncing-a-self-improving-ai-agent-across-machines.png
-banner: /banners/syncing-a-self-improving-ai-agent-across-machines.png
+ogImage: /og/zh-syncing-a-self-improving-ai-agent-across-machines.jpg
+banner: /banners/syncing-a-self-improving-ai-agent-across-machines.jpg
 ---
 
 我的 agent 会学习。每当我带它走一遍不平凡的工作流程——如何发布到 Gitea、如何排查一个时好时坏的 Docker 容器、如何写一条 Shopee 商品列表——它就会把过程存成一项 *skill*：一个下次遇到同类任务时自动加载的可复用流程。几个月下来，它累积了 172 项技能，横跨二十个分类。它们就是我的第二大脑。