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/l10n/gen/app_localizations_fr.dart

@@ -753,6 +753,9 @@ class AppLocalizationsFr extends AppLocalizations {
   @override
   String get openFullPlayerTooltip => 'Ouvrir le lecteur complet';
 
+  @override
+  String get nowListeningLabel => 'En cours d\'écoute';
+
   @override
   String get nothingPlayingTitle => 'Rien n\'est en cours de lecture';
 
@@ -792,6 +795,9 @@ class AppLocalizationsFr extends AppLocalizations {
   @override
   String get exploreNewSubtitle => 'Cette semaine';
 
+  @override
+  String get popularNowTitle => 'Populaire maintenant';
+
   @override
   String get offlineBannerTitle => 'Aucune connexion';