feat: season title card on cold start

Shows "SEASON 1 / First Bloom / N stages" over the season background for
~1.6s between splash and home; tap anywhere skips. Bails to home on
content-load error. Adds seasonLabel/seasonStages l10n keys (en + ko).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/ui/screens/splash_screen.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
 
-import 'home_screen.dart';
+import 'season_title_screen.dart';
 
-Widget _defaultNextScreen() => const HomeScreen();
+Widget _defaultNextScreen() => const SeasonTitleScreen();
 
 /// Logo-assembly splash: four glossy blocks fly in to form a 2x2 mark, the
 /// wordmark fades in, then we hand off. SaveRepository is already opened in