Add bakery.toml and packaging/arch to match bread ecosystem

Mirrors the build/distribution pattern used by the bread project:
- bakery.toml describes bos-settings as a bakery-managed package
- packaging/arch/PKGBUILD builds and installs the binary via cargo
- packaging/arch/bos-settings.desktop for app launchers
- LICENSE (MIT) required by PKGBUILD

packaging/arch/PKGBUILD

@@ -0,0 +1,34 @@
+# Maintainer: Breadway <rileyhorsham@gmail.com>
+
+pkgname=bos-settings
+pkgver=0.1.0
+pkgrel=1
+pkgdesc="System settings app for Bread OS"
+arch=('x86_64')
+url="https://github.com/Breadway/bos"
+license=('MIT')
+depends=('gtk4' 'glib2' 'hicolor-icon-theme')
+optdepends=(
+  'snapper: snapshot management view'
+)
+makedepends=('rust' 'cargo')
+source=("${pkgname}-${pkgver}.tar.gz")
+sha256sums=('SKIP')
+
+build() {
+  cd "${srcdir}/${pkgname}-${pkgver}"
+  cargo build --release --locked -p bos-settings
+}
+
+check() {
+  cd "${srcdir}/${pkgname}-${pkgver}"
+  cargo test --release --locked -p bos-settings
+}
+
+package() {
+  cd "${srcdir}/${pkgname}-${pkgver}"
+  install -Dm755 target/release/bos-settings "${pkgdir}/usr/bin/bos-settings"
+  install -Dm644 packaging/arch/bos-settings.desktop \
+    "${pkgdir}/usr/share/applications/bos-settings.desktop"
+  install -Dm644 LICENSE "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
+}

packaging/arch/README.md

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+Arch packaging
+==============
+
+`PKGBUILD` builds and installs `bos-settings` from source.
+
+## Local build
+
+```bash
+makepkg -si
+```
+
+## Before publishing to [breadway] repo
+
+1. Tag a release on GitHub.
+2. Update `pkgver` to match the tag.
+3. Update `source` to the release tarball URL.
+4. Run `updpkgsums` (or manually set `sha256sums`).
+
+## Runtime dependencies
+
+| Package | Required | Notes |
+|---------|----------|-------|
+| `gtk4` | yes | UI toolkit |
+| `glib2` | yes | always |
+| `snapper` | optional | snapshot management view |

packaging/arch/bos-settings.desktop

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+[Desktop Entry]
+Name=BOS Settings
+Comment=System settings for Bread OS
+Exec=bos-settings
+Icon=preferences-system
+Terminal=false
+Type=Application
+Categories=Settings;System;
+StartupWMClass=bos-settings