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/src/config.rs

@@ -0,0 +1,135 @@
+use anyhow::{Context, Result};
+use serde::{Deserialize, Serialize};
+use std::fs;
+use std::path::{Path, PathBuf};
+
+/// Configuration stored in `~/.config/bread/sync.toml`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SyncConfig {
+    pub remote: RemoteConfig,
+    pub machine: MachineConfig,
+    #[serde(default)]
+    pub packages: PackagesConfig,
+    #[serde(default)]
+    pub delegates: DelegatesConfig,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct RemoteConfig {
+    pub url: String,
+    #[serde(default = "default_branch")]
+    pub branch: String,
+}
+
+fn default_branch() -> String {
+    "main".to_string()
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct MachineConfig {
+    pub name: String,
+    #[serde(default)]
+    pub tags: Vec<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PackagesConfig {
+    #[serde(default = "default_true")]
+    pub enabled: bool,
+    #[serde(default)]
+    pub managers: Vec<String>,
+}
+
+fn default_true() -> bool {
+    true
+}
+
+impl Default for PackagesConfig {
+    fn default() -> Self {
+        Self {
+            enabled: true,
+            managers: vec![
+                "pacman".to_string(),
+                "pip".to_string(),
+                "npm".to_string(),
+                "cargo".to_string(),
+            ],
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct DelegatesConfig {
+    #[serde(default)]
+    pub include: Vec<String>,
+    #[serde(default)]
+    pub exclude: Vec<String>,
+}
+
+impl SyncConfig {
+    /// Load sync config from the given bread config directory.
+    pub fn load(config_dir: &Path) -> Result<Self> {
+        let path = config_dir.join("sync.toml");
+        let raw = fs::read_to_string(&path)
+            .with_context(|| "bread: sync not initialized. Run: bread sync init".to_string())?;
+        toml::from_str(&raw).context("failed to parse sync.toml")
+    }
+
+    /// Save sync config to the given bread config directory.
+    pub fn save(&self, config_dir: &Path) -> Result<()> {
+        let path = config_dir.join("sync.toml");
+        fs::create_dir_all(config_dir)?;
+        let raw = toml::to_string_pretty(self).context("failed to serialize sync config")?;
+        fs::write(&path, raw).with_context(|| format!("failed to write {}", path.display()))
+    }
+
+    /// Returns the local sync repo path (`~/.local/share/bread/sync-repo/`).
+    pub fn local_repo_path() -> PathBuf {
+        if let Some(data_dir) = dirs::data_dir() {
+            return data_dir.join("bread").join("sync-repo");
+        }
+        // Fallback using $HOME
+        if let Ok(home) = std::env::var("HOME") {
+            return PathBuf::from(home)
+                .join(".local")
+                .join("share")
+                .join("bread")
+                .join("sync-repo");
+        }
+        PathBuf::from(".local/share/bread/sync-repo")
+    }
+}
+
+/// Returns the bread config directory (`~/.config/bread/`).
+pub fn bread_config_dir() -> PathBuf {
+    if let Some(cfg) = dirs::config_dir() {
+        return cfg.join("bread");
+    }
+    if let Ok(xdg) = std::env::var("XDG_CONFIG_HOME") {
+        return PathBuf::from(xdg).join("bread");
+    }
+    if let Ok(home) = std::env::var("HOME") {
+        return PathBuf::from(home).join(".config").join("bread");
+    }
+    PathBuf::from(".config/bread")
+}
+
+/// Expand `~` to the home directory in a path string.
+pub fn expand_path(path: &str) -> PathBuf {
+    if path == "~" {
+        if let Some(home) = dirs::home_dir() {
+            return home;
+        }
+        if let Ok(home) = std::env::var("HOME") {
+            return PathBuf::from(home);
+        }
+    } else if let Some(rest) = path.strip_prefix("~/") {
+        if let Some(home) = dirs::home_dir() {
+            return home.join(rest);
+        }
+        if let Ok(home) = std::env::var("HOME") {
+            return PathBuf::from(home).join(rest);
+        }
+    }
+    PathBuf::from(path)
+}