fix(vacaciones): replace the progress bar with the prototype's date pair

Item 21 / audit 9b.4-9b.5 (t4:451-462, 469-479): the active vacation
range showed a LinearProgressIndicator the prototype never draws.
Replace it with the screen's real signature element -- a start/end
date pair (day+month, weekday, connector rule) -- reused with a flat
connector for the "programados"/"pasados" rows, replacing their plain
ListTiles with proper cards.

lib/l10n/formato_fechas.dart

@@ -11,3 +11,14 @@ import 'package:intl/intl.dart';
 /// this safely.
 String fechaCortaLocalizada(String localeTag, DateTime fecha) =>
     DateFormat.yMd(localeTag).format(fecha);
+
+/// Day + abbreviated month, locale-aware (e.g. "28 jul" for `es`, "Jul 28"
+/// for `en`) — item 21 / audit 9b.4 (t4:459), the big digit half of the
+/// vacation screen's date-pair.
+String diaMesLocalizado(String localeTag, DateTime fecha) =>
+    DateFormat.MMMd(localeTag).format(fecha);
+
+/// Full weekday name, locale-aware (e.g. "lunes"/"Monday") — item 21 /
+/// audit 9b.4 (t4:459), the small caption under the day-month.
+String nombreDiaSemanaLocalizado(String localeTag, DateTime fecha) =>
+    DateFormat.EEEE(localeTag).format(fecha);