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.

bread-sync/README.md

@@ -0,0 +1,88 @@
+# bread-sync
+
+Sync engine for [Bread](../README.md) — snapshot and restore desktop state via a Git remote.
+
+## Purpose
+
+`bread-sync` provides the library backing `bread sync` commands. It handles:
+
+- **Git operations** — clone, commit, push, pull, fetch, diff via `git2`
+- **Config serialization** — read/write `sync.toml` (machine name, remote URL, delegates, packages)
+- **Delegate file sync** — rsync-style directory copy with glob excludes
+- **Package snapshots** — capture installed packages from pacman, pip, npm, cargo
+- **Machine profiles** — per-machine TOML records with hostname, tags, and last-sync timestamp
+
+## Public API
+
+### `config`
+
+```rust
+SyncConfig::load(config_dir: &Path) -> Result<SyncConfig>
+SyncConfig::save(&self, config_dir: &Path) -> Result<()>
+SyncConfig::local_repo_path() -> PathBuf   // ~/.local/share/bread/sync-repo/
+bread_config_dir() -> PathBuf              // ~/.config/bread/
+expand_path(path: &str) -> PathBuf         // expands ~/
+```
+
+### `git`
+
+```rust
+SyncRepo::init(path: &Path) -> Result<SyncRepo>
+SyncRepo::open(path: &Path) -> Result<SyncRepo>
+SyncRepo::clone_from(url: &str, path: &Path) -> Result<SyncRepo>
+SyncRepo::open_or_clone(url: &str, path: &Path) -> Result<SyncRepo>
+SyncRepo::commit(&self, message: &str) -> Result<Option<git2::Oid>>  // None = nothing to commit
+SyncRepo::push(&self, remote: &str, branch: &str) -> Result<()>
+SyncRepo::pull(&self, remote: &str, branch: &str) -> Result<()>      // fast-forward only
+SyncRepo::fetch(&self, remote: &str, branch: &str) -> Result<()>
+SyncRepo::is_clean(&self) -> Result<bool>
+SyncRepo::local_changes(&self) -> Result<Vec<(char, String)>>
+SyncRepo::remote_changes(&self, remote: &str, branch: &str) -> Result<Vec<(char, String)>>
+SyncRepo::working_diff(&self) -> Result<String>
+SyncRepo::remote_diff(&self, remote: &str, branch: &str) -> Result<String>
+SyncRepo::set_remote(&self, name: &str, url: &str) -> Result<()>
+SyncRepo::last_commit_time(&self) -> Option<DateTime<Local>>
+```
+
+### `delegates`
+
+```rust
+sync_dir(src: &Path, dst: &Path, exclude: &[String]) -> Result<()>
+resolve_include_paths(includes: &[String]) -> Vec<(String, PathBuf)>
+```
+
+### `machine`
+
+```rust
+MachineProfile::new(name: String, tags: Vec<String>) -> MachineProfile
+MachineProfile::write(&self, machines_dir: &Path) -> Result<()>
+MachineProfile::read(machines_dir: &Path, name: &str) -> Result<MachineProfile>
+MachineProfile::list(machines_dir: &Path) -> Result<Vec<MachineProfile>>
+hostname() -> String
+```
+
+### `packages`
+
+```rust
+snapshot(manager: &str, dest: &Path) -> Result<bool>  // false = manager not found (non-fatal)
+parse_pacman(content: &str) -> Vec<String>
+parse_pip(content: &str) -> Vec<String>
+parse_npm(content: &str) -> Vec<String>
+parse_cargo(content: &str) -> Vec<String>
+```
+
+## Sync repo layout
+
+```
+~/.local/share/bread/sync-repo/
+├── bread/          ← snapshot of ~/.config/bread/
+├── configs/
+│   └── <basename>/ ← delegate paths
+├── machines/
+│   └── <name>.toml ← per-machine profiles
+└── packages/
+    ├── pacman.txt
+    ├── pip.txt
+    ├── npm.txt
+    └── cargo.txt
+```