plate-test: app-neutral print color scenes, checked by PDF structure and Ghostscript plates

craft-plate-test writes JSON scenes through craft-pdf and checks the written PDF's
structure (CI, under a second) and, locally only, its separated plates through
Ghostscript tiffsep (scripts/plate-check.sh). Apps can run the same scenes through
their own export as a dev-dependency.

scripts/plate-check.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+# Separate every plate-test scene with Ghostscript (local only, never CI) and judge the plates.
+# Ghostscript is `gs` on PATH, or CRAFT_PLATE_TEST_GS.
+set -euo pipefail
+root=$(cd "$(dirname "$0")/.." && pwd)
+fonts="${XDG_CACHE_HOME:-$HOME/.cache}/craft-pdf-test-fonts"
+if [[ -z "${CRAFT_PDF_TEST_FONT_DIR:-}" && -f "$fonts/Inter-Regular.ttf" ]]; then
+  export CRAFT_PDF_TEST_FONT_DIR="$fonts"
+fi
+cd "$root"
+cargo test -p craft-plate-test --test ghostscript -- --ignored --nocapture
+echo "report: ${CARGO_TARGET_DIR:-target}/plate-test/report.md"