Seed from go-template-repo, renamed to simplexcalc

The template's files at a77fd30, without its history or LICENSE, after
script/rename simplexcalc.

Model: opus-5-5

script/prettier

@@ -0,0 +1,52 @@
+#!/bin/sh
+# script/prettier: run prettier over this repo with the repo's own
+# .prettierrc. Helper, not an entrypoint: script/fmt and
+# script/fmt-check call it.
+#
+# Prettier from PATH if it is there, otherwise a hash-pinned node image
+# via docker, so a checkout with neither node nor a global prettier
+# still formats identically. If neither is available the caller is told
+# and the markdown pass is skipped rather than silently passing — a
+# formatter that is not present cannot certify formatting.
+#
+# Exit status: prettier's own, 2 when it was skipped for lack of a
+# runner. script/fmt-check treats 2 as a warning, not a failure, so
+# that `make check` still works on a machine without docker.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+# node:24-alpine, 2026-08-22. Bumping the pin is a deliberate edit.
+NODE_IMAGE="node:24-alpine@sha256:d32cdf619f63fe0471182d08996dd516c6275bb5fd31ae06e55a570bd9e1ad43"
+
+# Pinned exactly: prettier's default formatting changes between minor
+# releases, so an unpinned version turns fmt-check into a coin flip.
+PRETTIER_VERSION="3.9.6"
+
+main() {
+    cd "$ROOT"
+
+    if command -v prettier >/dev/null 2>&1; then
+        prettier "$@"
+        return $?
+    fi
+
+    if command -v docker >/dev/null 2>&1; then
+        # --user keeps written files owned by the invoking user rather
+        # than root; the container only ever touches the bind mount.
+        docker run --rm \
+            --user "$(id -u):$(id -g)" \
+            -v "$ROOT:/work" \
+            -w /work \
+            "$NODE_IMAGE" \
+            npx --yes "prettier@$PRETTIER_VERSION" "$@"
+        return $?
+    fi
+
+    echo "script/prettier: neither prettier nor docker found;" >&2
+    echo "script/prettier: skipping markdown/CSS/JS formatting." >&2
+
+    return 2
+}
+
+main "$@"