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/l10n/app_en.arb

@@ -28,5 +28,14 @@
         "type": "int"
       }
     }
+  },
+  "seasonLabel": "SEASON",
+  "seasonStages": "{count} stages",
+  "@seasonStages": {
+    "placeholders": {
+      "count": {
+        "type": "int"
+      }
+    }
   }
 }