ci: port breadbar onto shared bread-ecosystem build system

Delegates dev/rc/release build steps to bread-ecosystem's pinned Arch
container via ci/build.sh, pinned to bread-ecosystem commit
147cfbbf96ae4b171027defa1130d2caddb934b1. Adds a check.yml workflow
for fast clippy/test signal on feature/fix branches, matching the
pattern proven in breadpad. No ci/deps.txt needed — breadbar's
dependencies (zbus, resvg, gtk4-layer-shell, hyprland) are all pure
Rust or already covered by the shared image's package set.

ci/bread-ecosystem.rev

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+147cfbbf96ae4b171027defa1130d2caddb934b1

ci/build.sh

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+#!/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 "${CACHE_DIR}/ci/build.sh" breadbar "$ROOT" "$@"