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

List/Select skills with $-mention or /skills

codex-rs/tui/src/app_backtrack.rs

@@ -347,6 +347,7 @@ impl App {
             enhanced_keys_supported: self.enhanced_keys_supported,
             auth_manager: self.auth_manager.clone(),
             feedback: self.feedback.clone(),
+            skills: self.skills.clone(),
             is_first_run: false,
         };
         self.chat_widget =