feat(tokens): add design tokens, type scale, push scaffold, and root nav state

lib/estado/estado_navegacion.dart

@@ -0,0 +1,24 @@
+import 'package:flutter/foundation.dart';
+
+/// The five root tabs, in their declared (and displayed) order. Declaration
+/// order IS the tab order — the single source shared by `_paginas` and
+/// `_navItems` in app.dart (Design ADR-8).
+enum RaizPluriWave { escuchar, buscar, favoritos, alarmas, ajustes }
+
+/// Root-to-root navigation state (Design ADR-8). The single source of truth
+/// for which of the 5 root tabs is active. Switching roots is a plain
+/// notifier update — it never pushes a route.
+class EstadoNavegacionRaiz extends ChangeNotifier {
+  RaizPluriWave _actual = RaizPluriWave.escuchar;
+
+  RaizPluriWave get actual => _actual;
+
+  /// Declaration order doubles as the bottom-nav index.
+  int get indice => _actual.index;
+
+  void irA(RaizPluriWave raiz) {
+    if (raiz == _actual) return;
+    _actual = raiz;
+    notifyListeners();
+  }
+}