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_ja.dart

@@ -720,6 +720,9 @@ class AppLocalizationsJa extends AppLocalizations {
   @override
   String get openFullPlayerTooltip => 'フルプレーヤーを開く';
 
+  @override
+  String get nowListeningLabel => '再生中';
+
   @override
   String get nothingPlayingTitle => 'まだ何も再生されていません';
 
@@ -758,6 +761,9 @@ class AppLocalizationsJa extends AppLocalizations {
   @override
   String get exploreNewSubtitle => '今週';
 
+  @override
+  String get popularNowTitle => '今人気';
+
   @override
   String get offlineBannerTitle => '接続なし';