feat(i18n): 다국어 번역 확장 및 UI 개선

- 영어/일본어/한국어/중국어 번역 추가
- VictoryOverlay 레이아웃 개선
- NewCharacterScreen 기능 추가

lib/src/features/new_character/new_character_screen.dart

@@ -2,6 +2,7 @@ import 'dart:math' as math;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart' show FilteringTextInputFormatter;
 
 import 'package:asciineverdie/data/class_data.dart';
 import 'package:asciineverdie/data/game_text_l10n.dart' as game_l10n;
@@ -398,6 +399,10 @@ class _NewCharacterScreenState extends State<NewCharacterScreen> {
                 fontSize: 10,
                 color: RetroColors.textLight,
               ),
+              // 영문 알파벳만 허용 (공백 불가)
+              inputFormatters: [
+                FilteringTextInputFormatter.allow(RegExp(r'[a-zA-Z]')),
+              ],
               decoration: InputDecoration(
                 labelText: l10n.name,
                 labelStyle: const TextStyle(