fix(escuchar,reproductor): add the section-heading token and screen 1-3 polish

Audit S7 plus the open items on screens 1-3. Escuchar gains the
prototype's own 52px "now listening" eyebrow header (t4:53), which is
structurally different from the 56px title row every other root uses
(t4:325) -- the earlier wiring test asserted PluriRootHeader on all five
roots, an over-broad premise now corrected to guard what actually holds:
no AppBar, and the sleep-timer action still reachable.

test/pantallas/root_header_wiring_test.dart

@@ -102,8 +102,19 @@ void main() {
   );
 
   testWidgets(
-    'Escuchar draws its own PluriRootHeader with the tab title, no AppBar',
+    'Escuchar is the documented header exception: a 52px "now listening" '
+    'eyebrow instead of a PluriRootHeader title row, and still no AppBar',
     (tester) async {
+      // The prototype gives Escuchar a STRUCTURALLY different header from
+      // every other root (t4 line 53 vs line 325): 52px rather than 56, an
+      // eyebrow at 15px/w800/55% opacity rather than a 23px title, and
+      // trailing actions rather than a CTA. This test originally asserted
+      // `PluriRootHeader` on all five roots — an over-broad premise, since
+      // Escuchar's header was never a title row in the design.
+      //
+      // What still holds unconditionally, and is what this guards: no
+      // AppBar anywhere (systemic item S1), and the sleep-timer action that
+      // used to live in the removed global chrome is still reachable here.
       _suppressListTileInkAssertion();
       setLargeSurface(tester);
       final estado = crearEstadoRadio();
@@ -112,9 +123,18 @@ void main() {
       await tester.pumpWidget(testApp(estado, const PantallaInicio()));
       await pumpStable(tester);
 
-      expect(find.byType(PluriRootHeader), findsOneWidget);
-      expect(titleInHeader('Listen'), findsOneWidget);
       expect(find.byType(AppBar), findsNothing);
+      expect(
+        find.byType(PluriRootHeader),
+        findsNothing,
+        reason: 'Escuchar uses its own eyebrow header, not the shared one',
+      );
+      expect(find.text('Now listening'), findsOneWidget);
+      expect(
+        find.byIcon(Icons.bedtime_outlined),
+        findsOneWidget,
+        reason: 'the sleep-timer action survived the global AppBar removal',
+      );
     },
   );