feat: rewrite moonset in Rust (gtk4-rs + gtk4-layer-shell)

Feature-parity with Python v0.2.0. Same CSS, same UI, same actions.
Single 3.1 MB binary with embedded resources (CSS, wallpaper, avatar).

Modules: power.rs, i18n.rs, config.rs, users.rs, panel.rs, main.rs
45 unit tests passing. Python sources retained as reference.

src/users.rs

@@ -0,0 +1,141 @@
+// ABOUTME: Current user detection and avatar loading for the power menu.
+// ABOUTME: Retrieves user info from the system (pwd, AccountsService, ~/.face).
+
+use nix::unistd::{getuid, User as NixUser};
+use std::path::{Path, PathBuf};
+
+const DEFAULT_ACCOUNTSSERVICE_DIR: &str = "/var/lib/AccountsService/icons";
+const GRESOURCE_PREFIX: &str = "/dev/moonarch/moonset";
+
+/// Represents the current user for the power menu.
+#[derive(Debug, Clone)]
+pub struct User {
+    pub username: String,
+    pub display_name: String,
+    pub home: PathBuf,
+    pub uid: u32,
+}
+
+/// Get the currently logged-in user's info from the system.
+pub fn get_current_user() -> Option<User> {
+    let uid = getuid();
+    let nix_user = NixUser::from_uid(uid).ok()??;
+
+    let gecos = nix_user.gecos.to_str().unwrap_or("").to_string();
+    // GECOS field may contain comma-separated values; first field is the full name
+    let display_name = if !gecos.is_empty() {
+        let first = gecos.split(',').next().unwrap_or("");
+        if first.is_empty() {
+            nix_user.name.clone()
+        } else {
+            first.to_string()
+        }
+    } else {
+        nix_user.name.clone()
+    };
+
+    Some(User {
+        username: nix_user.name,
+        display_name,
+        home: nix_user.dir,
+        uid: uid.as_raw(),
+    })
+}
+
+/// Find the user's avatar image, checking ~/.face then AccountsService.
+pub fn get_avatar_path(home: &Path, username: Option<&str>) -> Option<PathBuf> {
+    get_avatar_path_with(home, username, Path::new(DEFAULT_ACCOUNTSSERVICE_DIR))
+}
+
+/// Find avatar with configurable AccountsService dir (for testing).
+pub fn get_avatar_path_with(
+    home: &Path,
+    username: Option<&str>,
+    accountsservice_dir: &Path,
+) -> Option<PathBuf> {
+    // ~/.face takes priority
+    let face = home.join(".face");
+    if face.exists() {
+        return Some(face);
+    }
+
+    // AccountsService icon
+    if let Some(name) = username {
+        if accountsservice_dir.exists() {
+            let icon = accountsservice_dir.join(name);
+            if icon.exists() {
+                return Some(icon);
+            }
+        }
+    }
+
+    None
+}
+
+/// Return the GResource path to the default avatar SVG.
+pub fn get_default_avatar_path() -> String {
+    format!("{GRESOURCE_PREFIX}/default-avatar.svg")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+
+    #[test]
+    fn get_current_user_returns_some() {
+        let user = get_current_user();
+        assert!(user.is_some());
+        let user = user.unwrap();
+        assert!(!user.username.is_empty());
+        assert!(!user.display_name.is_empty());
+        assert!(user.home.exists());
+    }
+
+    #[test]
+    fn returns_face_file_if_exists() {
+        let dir = tempfile::tempdir().unwrap();
+        let face = dir.path().join(".face");
+        fs::write(&face, "fake image").unwrap();
+        let path = get_avatar_path_with(dir.path(), None, Path::new("/nonexistent"));
+        assert_eq!(path, Some(face));
+    }
+
+    #[test]
+    fn returns_accountsservice_icon_if_exists() {
+        let dir = tempfile::tempdir().unwrap();
+        let icons_dir = dir.path().join("icons");
+        fs::create_dir(&icons_dir).unwrap();
+        let icon = icons_dir.join("testuser");
+        fs::write(&icon, "fake image").unwrap();
+        let path = get_avatar_path_with(dir.path(), Some("testuser"), &icons_dir);
+        assert_eq!(path, Some(icon));
+    }
+
+    #[test]
+    fn face_file_takes_priority_over_accountsservice() {
+        let dir = tempfile::tempdir().unwrap();
+        let face = dir.path().join(".face");
+        fs::write(&face, "fake image").unwrap();
+        let icons_dir = dir.path().join("icons");
+        fs::create_dir(&icons_dir).unwrap();
+        let icon = icons_dir.join("testuser");
+        fs::write(&icon, "fake image").unwrap();
+        let path = get_avatar_path_with(dir.path(), Some("testuser"), &icons_dir);
+        assert_eq!(path, Some(face));
+    }
+
+    #[test]
+    fn returns_none_when_no_avatar() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = get_avatar_path_with(dir.path(), None, Path::new("/nonexistent"));
+        assert!(path.is_none());
+    }
+
+    #[test]
+    fn default_avatar_path_is_gresource() {
+        let path = get_default_avatar_path();
+        assert!(path.contains("default-avatar.svg"));
+        assert!(path.starts_with("/dev/moonarch/moonset"));
+    }
+}