www.yml: regenerate og:image mosaic in CI

`compose-og.sh` (stations map + 2 plots → 1200×630
`ctbk-og-mosaic.jpg`, the `og:image` since `f0545db2`) was manual-only
— the shipped mosaic was 4 months stale while its source screenshots
regenerated on every deploy. Run it in www.yml right after the
screenshot step; exclude it from the change-gate (like
`ctbk-stations`, whose per-run map-render variance would re-trigger
the commit-back loop forever) so it ships whenever a plot screenshot
actually changes — i.e. every data-driven deploy, ≈monthly.

`compose-og.sh` gains a `magick`/`convert` shim (GHA ubuntu runners
have ImageMagick 6).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ryan-williams

.github/workflows/www.yml

@@ -57,11 +57,20 @@ jobs:
         with:
           name: screenshots
           path: www/public/screenshots/
+      - name: Compose og:image mosaic
+        working-directory: www
+        # Recomposes `ctbk-og-mosaic.jpg` from the just-regenerated
+        # screenshots (map + 2 plots). Excluded from the change-gate below
+        # (like `ctbk-stations`) because the map render varies per run —
+        # gating on it would re-trigger forever. It still ships whenever a
+        # PLOT screenshot changes (monthly data updates), riding the same
+        # commit.
+        run: bash scripts/compose-og.sh
       - name: Push + re-run, if screenshots changed
         if: github.ref == 'refs/heads/www'
         id: screenshots
         run: |
-          if git diff --name-only -- www/public/screenshots | grep -v ctbk-stations; then
+          if git diff --name-only -- www/public/screenshots | grep -v -e ctbk-stations -e ctbk-og-mosaic; then
               git add www/public/screenshots
               git config --global user.name "GitHub Actions"
               git config --global user.email "github@actions"

www/scripts/compose-og.sh

@@ -1,9 +1,12 @@
 #!/bin/bash
 # Compose an og:image mosaic: dark stations map (left) + 2 stacked DM plots (right)
 # Layout: map fills left ~70%, 2 near-square plots on right ~30% with gap between.
-# Requires: ImageMagick (magick)
+# Requires: ImageMagick — v7 (`magick`) or v6 (`convert`, e.g. ubuntu GHA runners)
 set -e
 
+MAGICK="$(command -v magick || command -v convert)"
+magick() { "$MAGICK" "$@"; }
+
 cd "$(dirname "$0")/.."
 
 SS=public/screenshots