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/app_es.arb

@@ -358,6 +358,7 @@
   "yourStationsTitle": "Tus emisoras",
   "seeAllAction": "Ver todas",
   "openFullPlayerTooltip": "Abrir reproductor completo",
+  "nowListeningLabel": "Escuchando ahora",
   "nothingPlayingTitle": "Todavía no estás escuchando nada",
   "nothingPlayingSubtitle": "Elegí una emisora de Tus emisoras o buscá una para empezar.",
   "nearYou": "Cerca de vos",
@@ -375,6 +376,7 @@
   "exploreTrendingSubtitle": "Hoy",
   "exploreNewTitle": "Novedades",
   "exploreNewSubtitle": "Esta semana",
+  "popularNowTitle": "Populares ahora",
   "offlineBannerTitle": "Sin conexión",
   "retryAction": "Reintentar",
   "noStationsAvailable": "No hay emisoras disponibles",