fix(upgrade): errors from Rust 2024 edition

- gen is a reserved keyword (→ renamed module to generator)
- ref in patterns with implicit borrowing (→ removed ref)
- & pattern with implicit borrowing (→ added & to outer pattern)

src/main.rs

@@ -371,7 +371,7 @@ fn run_headless_script(script_path: &PathBuf, file: &Option<PathBuf>) -> Result<
 // ── Helpers ──────────────────────────────────────────────────────────────────
 
 fn get_initial_model(file_path: &Option<PathBuf>) -> Result<Model> {
-    if let Some(ref path) = file_path {
+    if let Some(path) = file_path {
         if path.exists() {
             let mut m = persistence::load(path)
                 .with_context(|| format!("Failed to load {}", path.display()))?;