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/README.md

@@ -41,4 +41,46 @@ No entry → a generic default terminal.
 
 - PNG (not JPG) is intentional: for flat UI/terminal art, PNG is smaller and
   sharper than JPG (see commit history).
-- The `logo-square.png` referenced lives at `public/logo-square.png`.
+- The `logo-square.png` referenced lives at `public/logo-square.png`.
+---
+
+## v2 pipeline ("one art, four targets") — `render_from_art.mjs`
+
+The consultant-approved redesign replaces the generated terminal panels with **one
+zero-text base-art frame per post**, composited into four assets:
+
+| Target | Path | Size |
+|---|---|---|
+| hero banner | `public/banners/<slug>.webp` (+ `.jpg` fallback from frontmatter) | 1600×900 |
+| social card | `public/og/<slug>.jpg` (EN), `public/og/zh-<slug>.jpg` (ZH) | 1200×630 |
+| bento/list thumb | `public/og/thumb/<slug>-800.webp` | 800×420 |
+| small thumb | `public/og/thumb/<slug>-400.webp` | 400×210 |
+
+The card is `template-v2.2.html` (frosted bento + blueprint grid + full-width evidence
+bar) filled from the post's own frontmatter plus `art-meta.json`; the self-fitting
+headline script reports `FIT <n>px` through `<title>`, and a render that does not
+settle fails instead of shipping a silently-shrunken card.
+
+```bash
+# metadata first: art path (default <art-dir>/<slug>.png) + a HAND-WRITTEN evidence line
+$EDITOR scripts/og-gen/art-meta.json
+
+node scripts/og-gen/render_from_art.mjs --only <slug>[,<slug>] --out /tmp/og-check
+node scripts/og-gen/render_from_art.mjs --all            # writes into public/
+```
+
+- `--format jpg` (default) or `png`. **JPEG is the default because it is measured**:
+  a composited card renders 558 KB as PNG and lands at **84 KB at mozjpeg q85**
+  (256-colour PNG = 240 KB). The default site card already ships as JPG for the
+  same reason.
+- `evidence` is **required and never derived** — it is editorial text, and inventing
+  one from the description is the "invented specificity" failure the blog avoids.
+  A missing entry aborts with the slug list.
+- `ogTitle_en` / `ogTitle_zh` shorten only the card's headline (the article keeps
+  its real title) — the consultant's answer to the English headline-rag problem.
+- Reproducibility check: re-rendering the two sample posts produced banners and
+  800px thumbs **byte-identical** to the consultant's accepted delivery
+  (sha256 16e6a7b0…, f3b29f38…, c4e28291…, 8095ec6c…).
+- ⚠ Changing `ogImage` from `.png` to `.jpg` also needs `PostList.astro`'s thumb
+  helper updated (`/\.(png|jpe?g)$/`), or the listing derives
+  `…-800.webp` from `slug.jpg` and every thumb 404s.