feat(og-gen): check in the v2 art pipeline and its batch renderer

The consultant-approved "one art, four targets" work existed only in the
working tree. Commit it so the 72-post rollout is reproducible from the repo
instead of from one session's scratch files.

- template-v2.html / v2.1 / v2.2: the iteration the consultant reviewed, plus
  the accepted frosted-bento layout (736x536 card, blueprint grid, full-width
  evidence bar, self-fitting headline script that reports "FIT <n>px").
- render_sample_suite{,_v2,_v3}.mjs + fit-title-probe.mjs: how the two sample
  posts were rendered for rounds 2-4 (kept for provenance).
- generate_prompts_catalog.py + prompts_catalog.json: the 72 per-post prompts
  and their visual metaphors, extracted from the posts themselves.
- render_from_art.mjs (new): the batch renderer. One zero-text base frame per
  post -> banner 1600x900 webp (+jpg fallback), social card 1200x630 (EN and
  zh-<slug>), thumbs 800x420 and 400x210. Cards are filled from frontmatter +
  art-meta.json; a missing evidence line or a headline that never settles is a
  hard failure, never a silently-degraded card.
- art-meta.json: the per-slug input contract. Two slugs wired; 70 still need
  base art (GPU) and a hand-written evidence line.
- README: documents the pipeline, the measured format choice (558 KB PNG ->
  84 KB mozjpeg q85) and the PostList thumb-helper trap when ogImage moves to
  .jpg.

Proof the renderer reproduces the accepted output: re-rendering the two sample
posts yields banner + 800px thumb files BYTE-IDENTICAL to the consultant's
delivery (sha256 16e6a7b0, f3b29f38, c4e28291, 8095ec6c), and all four cards
report FIT, 2-3 title lines, 2 description lines, 0 overflow in x and y.

scripts/og-gen/art-meta.json

@@ -0,0 +1,12 @@
+{
+  "_about": "Inputs for scripts/og-gen/render_from_art.mjs ('one art, four targets'). One entry per post: `art` = the zero-text base frame (default <art-dir>/<slug>.png), `evidence` = the short factual line shown in the card's evidence bar (REQUIRED, written by hand — never derived), optional `ogTitle_en` / `ogTitle_zh` = shortened display titles for the card only (consultant question 1, option C: the article keeps its real title), optional `tags` = override the three badge tags. Cards render from the post's own frontmatter (title/description/category) unless an ogTitle override is present.",
+  "_status": "2 of 72 posts have base art (the two consultant sample frames, reused). The remaining 70 need a GPU run from prompts_catalog.json before the batch can render.",
+  "running-production-infrastructure-solo": {
+    "art": "C:/AI/ideogram4/out/sample_prod_169_00001_.png",
+    "evidence": "162 containers · 3 hosts · 78 compose stacks"
+  },
+  "docker-reported-exit-0-the-oom-killer-disagreed": {
+    "art": "C:/AI/ideogram4/out/sample_oom_169_00001_.png",
+    "evidence": "exit 0 · dmesg: 6x cgroup OOM kills"
+  }
+}