Rewrite init script in rust and fix non-shell CMDs

src/registry.rs

@@ -32,6 +32,12 @@ pub(crate) fn registry_base_dir() -> Result<PathBuf> {
         .context("Failed to create XDG_DATA_HOME subdirectory")
 }
 
+pub(crate) fn init_binary_path() -> Result<PathBuf> {
+    let base = xdg::BaseDirectories::with_prefix("slim-rs");
+    base.get_data_file("slim-init")
+        .context("slim-init not found in XDG data dir")
+}
+
 pub(crate) fn registry_dir(image: &str) -> Result<PathBuf> {
     validate_image_name(image)?;
     let base = registry_base_dir()?;