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

bakery.toml

@@ -0,0 +1,12 @@
+name = "bos-settings"
+description = "System settings app for Bread OS"
+binaries = ["bos-settings"]
+system_deps = ["gtk4", "glib2"]
+optional_system_deps = ["snapper"]
+bread_deps = []
+
+[config]
+dir = "~/.config"
+
+[install]
+post_install = []