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.

lib/tema/pluriwave_typography.dart

@@ -2,8 +2,11 @@ import 'package:flutter/material.dart';
 
 /// Design ADR-1: the named type scale, split out of [PluriWaveTokens] into
 /// its own ThemeExtension so screens stop copy-pasting
-/// `.copyWith(fontWeight: w900, letterSpacing: …)`. The set is closed at six
-/// styles — a seventh requires amending ADR-1.
+/// `.copyWith(fontWeight: w900, letterSpacing: …)`. The set was closed at
+/// six styles; S7 (visual fidelity pass) amended ADR-1 to add a seventh —
+/// [inPageSectionHeading] — rather than have four screens each keep
+/// copy-pasting their own `titleMedium.copyWith(fontWeight: w900)` override,
+/// the exact duplication this extension exists to eliminate.
 ///
 /// [eyebrowLabel] never applies `toUpperCase()` — casing is a
 /// locale-hostile transform (Turkish dotless i, and scripts with no case at
@@ -18,6 +21,7 @@ class PluriWaveTypography extends ThemeExtension<PluriWaveTypography> {
     required this.cardTitle,
     required this.bodyStrong,
     required this.eyebrowLabel,
+    required this.inPageSectionHeading,
   });
 
   /// 88 / w800 / height 1.0 / ls -2.0. Alarm ringing, inline time editor.
@@ -41,6 +45,14 @@ class PluriWaveTypography extends ThemeExtension<PluriWaveTypography> {
   /// headers.
   final TextStyle eyebrowLabel;
 
+  /// 15 / w800 / ls -0.2. S7 (visual fidelity, t4 lines 80, 153, 164, 173):
+  /// an in-page section heading living directly on a screen's content —
+  /// "Tus emisoras", "Cerca de ti", "Explorar por", "Populares ahora".
+  /// Distinct from both [sectionTitle] (23, a ROOT screen's own title) and
+  /// [screenTitle] (19, a pushed screen's AppBar title) — this is smaller
+  /// than either, for a heading living one level below the screen itself.
+  final TextStyle inPageSectionHeading;
+
   /// Builds the scale from [family] — the SAME resolved Google Fonts
   /// TextTheme instance [PluriWaveTheme.dark] already computes. Building the
   /// styles anywhere else would re-merge the font family, which is the
@@ -79,6 +91,7 @@ class PluriWaveTypography extends ThemeExtension<PluriWaveTypography> {
         letterSpacing: 0.8,
         color: const Color(0xFFF2F7FA).withValues(alpha: 0.42),
       ),
+      inPageSectionHeading: style(15, FontWeight.w800, letterSpacing: -0.2),
     );
   }
 
@@ -90,6 +103,7 @@ class PluriWaveTypography extends ThemeExtension<PluriWaveTypography> {
     TextStyle? cardTitle,
     TextStyle? bodyStrong,
     TextStyle? eyebrowLabel,
+    TextStyle? inPageSectionHeading,
   }) {
     return PluriWaveTypography(
       heroTime: heroTime ?? this.heroTime,
@@ -98,6 +112,7 @@ class PluriWaveTypography extends ThemeExtension<PluriWaveTypography> {
       cardTitle: cardTitle ?? this.cardTitle,
       bodyStrong: bodyStrong ?? this.bodyStrong,
       eyebrowLabel: eyebrowLabel ?? this.eyebrowLabel,
+      inPageSectionHeading: inPageSectionHeading ?? this.inPageSectionHeading,
     );
   }
 
@@ -117,6 +132,9 @@ class PluriWaveTypography extends ThemeExtension<PluriWaveTypography> {
       bodyStrong: TextStyle.lerp(bodyStrong, other.bodyStrong, t) ?? bodyStrong,
       eyebrowLabel:
           TextStyle.lerp(eyebrowLabel, other.eyebrowLabel, t) ?? eyebrowLabel,
+      inPageSectionHeading:
+          TextStyle.lerp(inPageSectionHeading, other.inPageSectionHeading, t) ??
+          inPageSectionHeading,
     );
   }
 }