feat(tui): implement live model fetching and enhance model selection menus

src/interfaces/tui/state.ts

@@ -384,6 +384,8 @@ export class MiscState {
   activity: ActivityEntry[] = [];
   /** Stack of interactive menu frames (top = currently shown). */
   menuStack: MenuFrame[] = [];
+  /** Model ids fetched live from the provider's /models endpoint. */
+  availableModels: string[] = [];
 
   pushToast(toast: { kind: string; message: string; createdMs: number; ttlMs: number }): void {
     this.toasts.push(toast);