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_ja.arb

@@ -816,5 +816,7 @@
   "welcomeBullet3Title": "音楽アラーム",
   "welcomeCtaLabel": "聴き始める",
   "welcomeHeadline": "あなたの世界を、ライブで",
-  "yourStationsTitle": "あなたの局"
+  "yourStationsTitle": "あなたの局",
+  "nowListeningLabel": "再生中",
+  "popularNowTitle": "今人気"
 }