CI: port breadhelp onto bread-ecosystem's shared Arch build container

Mirrors breadpad's proven pattern: ci/build.sh wraps bread-ecosystem's
shared ci/build.sh, pinned by commit sha in ci/bread-ecosystem.rev
(rev 147cfbbf96ae4b171027defa1130d2caddb934b1). No ci/deps.txt — the
shared image's gtk4/libadwaita/gtk4-layer-shell/graphene set already
covers breadhelp's dependency surface (no libadwaita or extra native
libs beyond those). dev-release.yml/rc-release.yml/release.yml now
build (and, in dev-release.yml, test) through ci/build.sh instead of
bare cargo on the runner; a new check.yml runs clippy+test on
feature/**/fix/** pushes as a fast pre-release signal.

ci/build.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# Delegates to bread-ecosystem's shared CI build image/script, pinned to
+# the commit in ci/bread-ecosystem.rev — not `main`. bread-ecosystem's CI
+# files now affect every product's release pipeline, so bumping the pin
+# is a deliberate act instead of silent drift (see the bread-theme test
+# that broke here for exactly that reason, before it was pinned by rev).
+#
+# Usage: ci/build.sh cargo build --release --locked
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+REV="$(cat "${ROOT}/ci/bread-ecosystem.rev")"
+
+CACHE_DIR="/tmp/bread-ecosystem-ci-${REV}"
+if [ ! -d "$CACHE_DIR" ]; then
+    rm -rf /tmp/bread-ecosystem-ci-*
+    git clone https://git.breadway.dev/Breadway/bread-ecosystem.git "$CACHE_DIR"
+    git -C "$CACHE_DIR" checkout --quiet "$REV"
+fi
+
+bash "${CACHE_DIR}/ci/build.sh" breadhelp "$ROOT" "$@"