feat: Support listing and selecting skills via $ or /skills (#7506)

List/Select skills with $-mention or /skills

codex-rs/tui/src/chatwidget/tests.rs

@@ -355,6 +355,7 @@ async fn helpers_are_available_and_do_not_panic() {
         enhanced_keys_supported: false,
         auth_manager,
         feedback: codex_feedback::CodexFeedback::new(),
+        skills: None,
         is_first_run: true,
     };
     let mut w = ChatWidget::new(init, conversation_manager);
@@ -380,6 +381,7 @@ fn make_chatwidget_manual() -> (
         placeholder_text: "Ask Codex to do anything".to_string(),
         disable_paste_burst: false,
         animations_enabled: cfg.animations,
+        skills: None,
     });
     let auth_manager = AuthManager::from_auth_for_testing(CodexAuth::from_api_key("test"));
     let widget = ChatWidget {