fix(buscar): rebuild the offline banner with offlineAccent

Audit 13.1 (t4 line 641): the banner rendered wifi_off in
colorScheme.error (red) inside a generic glass card. Rebuilt using
offlineAccent (#E8879A) — a token that existed since Tier 1 with no
consumer — for the tint, border and icon, plus the prototype's title/
detail layout and a restyled Retry chip. New offlineBannerTitle key
translated to all 13 locales.

lib/l10n/app_zh.arb

@@ -306,6 +306,7 @@
   "detectAction": "检测",
   "liveRadar": "直播雷达",
   "genresTitle": "类型",
+  "offlineBannerTitle": "无连接",
   "retryAction": "重试",
   "noStationsAvailable": "没有可用电台",
   "noStationsAvailableSubtitle": "尝试刷新或选择其他类型，重新捕捉信号。",