feat: add bread-sync module for snapshot and restore functionality

- Introduced `bread-sync` module with core functionalities for syncing system state via Git.
- Implemented `MachineProfile` struct for managing machine profiles, including methods for reading and writing profiles.
- Added package management support with snapshot capabilities for `pacman`, `pip`, `npm`, and `cargo`.
- Created comprehensive tests for sync operations, package parsing, and machine profile management.
- Enhanced `udev` adapter to include vendor and product IDs for scanned devices.
- Updated state engine to handle module clearing commands.
- Introduced Lua integration for accessing machine information and file system operations.
- Improved packaging documentation for Arch Linux and systemd service setup.

packaging/README.md

@@ -1,5 +1,47 @@
-Packaging notes
-================
+Packaging
+=========
 
-This repo targets Arch packaging. The Arch PKGBUILD skeleton lives under
-`packaging/arch/`.
+This directory contains distribution packaging for Bread.
+
+```
+packaging/
+├── arch/
+│   └── PKGBUILD          ← Arch Linux package build script
+└── systemd/
+    └── breadd.service    ← systemd user service unit
+```
+
+## Arch Linux
+
+```bash
+cd packaging/arch
+makepkg -si
+```
+
+The PKGBUILD builds both `breadd` and `bread` from source and installs them to `/usr/bin`. It also installs the systemd user service unit to `/usr/lib/systemd/user/`.
+
+Before publishing to the AUR, update `pkgver`, `source`, and `sha256sums` to point at a tagged release tarball.
+
+## systemd user service
+
+The service unit starts `breadd` as a user service after the graphical session is available.
+
+```bash
+# Install and enable manually (if not using the PKGBUILD)
+mkdir -p ~/.config/systemd/user
+cp systemd/breadd.service ~/.config/systemd/user/
+systemctl --user daemon-reload
+systemctl --user enable --now breadd
+
+# Check status
+systemctl --user status breadd
+journalctl --user -u breadd -f
+```
+
+The service sets `RUST_LOG=info` by default. To increase verbosity, override it in a drop-in:
+
+```ini
+# ~/.config/systemd/user/breadd.service.d/debug.conf
+[Service]
+Environment=RUST_LOG=debug
+```