art: v2 artwork for the 504 read-amplification post (6 targets)

Generated through post_art.py on the local RTX 3060. Metaphor: four identical
steel pipes drawing from one dark reservoir, plus a single short pipe that
bypasses all four into a lit chamber (four redundant reads vs the bypass path).

- banner 1600x900 from the planned crop (band 755,119-1281,675, x1.43, subject
  at 47.0% of the banner width) instead of the on-the-fly fallback
- EN + ZH OG cards, 800/400 list thumbs, banner webp
- evidence line: 4 reads/file - 960 per page - 0.3 us cache hit

State mirrored into the repo so git alone reproduces the frame: the caption,
plus this slug in metaphors.json and prompts_catalog.json. banner-plan.json
also picks up the 22 frames that were in art-meta but had no plan entry.

Verified: check-assets 190/190 with the post temporarily published, both pages
point at their own og card and banner, then reverted to draft true and rebuilt
-- no page left in dist. ComfyUI terminated after the render.

scripts/og-gen/art-meta.json

@@ -331,5 +331,8 @@
    "timeouts",
    "caching"
   ]
+ },
+ "read-amplification-504-gateway-timeout-swr-cache": {
+  "evidence": "4 reads/file · 960 per page · 0.3 µs cache hit"
  }
 }