fix: resolve test compilation errors and doctest issues

- Add HotkeysConfig::default() to Config initializers in tests
- Wrap env::set_var/remove_var calls in unsafe blocks
- Fix doctest in App::new() (select_chat -> select_current_chat)
- Mark TdClient doctest as ignore (async code needs runtime)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/app/mod.rs

@@ -41,7 +41,7 @@ use ratatui::widgets::ListState;
 /// app.previous_chat();
 ///
 /// // Open a chat
-/// app.select_chat();
+/// app.select_current_chat();
 /// ```
 pub struct App {
     pub config: crate::config::Config,