feat(ui): 화면 및 공통 위젯 개선

- FrontScreen 개선
- GamePlayScreen, GameSessionController 업데이트
- ArenaBattleScreen, NewCharacterScreen 정리
- AsciiDisintegrateWidget 추가

lib/src/shared/widgets/ascii_disintegrate_widget.dart

@@ -0,0 +1,219 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+
+/// ASCII 문자 분해 파티클
+class AsciiParticle {
+  AsciiParticle({
+    required this.char,
+    required this.initialX,
+    required this.initialY,
+    required this.vx,
+    required this.vy,
+    required this.delay,
+  }) : x = initialX,
+       y = initialY,
+       opacity = 1.0;
+
+  final String char;
+  final double initialX;
+  final double initialY;
+  final double vx; // X 속도
+  final double vy; // Y 속도
+  final double delay; // 분해 시작 지연 (0.0 ~ 0.3)
+
+  double x;
+  double y;
+  double opacity;
+
+  /// 진행도에 따라 파티클 상태 업데이트
+  void update(double progress) {
+    // 지연 적용
+    final adjustedProgress = ((progress - delay) / (1.0 - delay)).clamp(
+      0.0,
+      1.0,
+    );
+
+    if (adjustedProgress <= 0) {
+      // 아직 분해 시작 전
+      x = initialX;
+      y = initialY;
+      opacity = 1.0;
+      return;
+    }
+
+    // 이징 적용 (가속)
+    final easedProgress = Curves.easeOutQuad.transform(adjustedProgress);
+
+    // 위치 업데이트 (초기 위치에서 이동)
+    x = initialX + vx * easedProgress * 3.0;
+    y = initialY + vy * easedProgress * 3.0;
+
+    // 중력 효과
+    y += easedProgress * easedProgress * 2.0;
+
+    // 페이드 아웃 (후반부에 급격히)
+    opacity = (1.0 - easedProgress * easedProgress).clamp(0.0, 1.0);
+  }
+}
+
+/// ASCII 캐릭터 분해 애니메이션 위젯
+///
+/// 캐릭터의 각 ASCII 문자가 파티클로 분해되어 흩어지는 효과
+class AsciiDisintegrateWidget extends StatefulWidget {
+  const AsciiDisintegrateWidget({
+    super.key,
+    required this.characterLines,
+    this.charWidth = 8.0,
+    this.charHeight = 12.0,
+    this.duration = const Duration(milliseconds: 1500),
+    this.textColor,
+    this.onComplete,
+  });
+
+  /// ASCII 캐릭터 문자열 (줄 단위)
+  final List<String> characterLines;
+
+  /// 문자 너비 (픽셀)
+  final double charWidth;
+
+  /// 문자 높이 (픽셀)
+  final double charHeight;
+
+  /// 애니메이션 지속 시간
+  final Duration duration;
+
+  /// 텍스트 색상 (null이면 테마 색상)
+  final Color? textColor;
+
+  /// 완료 콜백
+  final VoidCallback? onComplete;
+
+  @override
+  State<AsciiDisintegrateWidget> createState() =>
+      _AsciiDisintegrateWidgetState();
+}
+
+class _AsciiDisintegrateWidgetState extends State<AsciiDisintegrateWidget>
+    with SingleTickerProviderStateMixin {
+  late AnimationController _controller;
+  late List<AsciiParticle> _particles;
+  final Random _random = Random();
+
+  @override
+  void initState() {
+    super.initState();
+    _initParticles();
+    _controller = AnimationController(duration: widget.duration, vsync: this)
+      ..addListener(() => setState(() {}))
+      ..addStatusListener((status) {
+        if (status == AnimationStatus.completed) {
+          widget.onComplete?.call();
+        }
+      })
+      ..forward();
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  void _initParticles() {
+    _particles = [];
+
+    for (int y = 0; y < widget.characterLines.length; y++) {
+      final line = widget.characterLines[y];
+      for (int x = 0; x < line.length; x++) {
+        final char = line[x];
+        // 공백은 파티클로 변환하지 않음
+        if (char != ' ') {
+          _particles.add(
+            AsciiParticle(
+              char: char,
+              initialX: x.toDouble(),
+              initialY: y.toDouble(),
+              // 랜덤 속도 (위쪽 + 좌우로 퍼짐)
+              vx: (_random.nextDouble() - 0.5) * 4.0,
+              vy: -_random.nextDouble() * 2.0 - 0.5, // 위쪽으로
+              // 랜덤 지연 (안쪽에서 바깥쪽으로 분해)
+              delay: _random.nextDouble() * 0.3,
+            ),
+          );
+        }
+      }
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    // 파티클 상태 업데이트
+    for (final particle in _particles) {
+      particle.update(_controller.value);
+    }
+
+    final textColor =
+        widget.textColor ?? Theme.of(context).textTheme.bodyMedium?.color;
+
+    return CustomPaint(
+      size: Size(
+        widget.characterLines.isNotEmpty
+            ? widget.characterLines
+                      .map((l) => l.length)
+                      .reduce((a, b) => a > b ? a : b) *
+                  widget.charWidth
+            : 0,
+        widget.characterLines.length * widget.charHeight,
+      ),
+      painter: _DisintegratePainter(
+        particles: _particles,
+        charWidth: widget.charWidth,
+        charHeight: widget.charHeight,
+        textColor: textColor ?? Colors.white,
+      ),
+    );
+  }
+}
+
+/// 분해 파티클 페인터
+class _DisintegratePainter extends CustomPainter {
+  _DisintegratePainter({
+    required this.particles,
+    required this.charWidth,
+    required this.charHeight,
+    required this.textColor,
+  });
+
+  final List<AsciiParticle> particles;
+  final double charWidth;
+  final double charHeight;
+  final Color textColor;
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    for (final particle in particles) {
+      if (particle.opacity <= 0) continue;
+
+      final textPainter = TextPainter(
+        text: TextSpan(
+          text: particle.char,
+          style: TextStyle(
+            fontFamily: 'JetBrainsMono',
+            fontSize: charHeight * 0.9,
+            color: textColor.withValues(alpha: particle.opacity),
+          ),
+        ),
+        textDirection: TextDirection.ltr,
+      )..layout();
+
+      final x = particle.x * charWidth;
+      final y = particle.y * charHeight;
+
+      textPainter.paint(canvas, Offset(x, y));
+    }
+  }
+
+  @override
+  bool shouldRepaint(covariant _DisintegratePainter oldDelegate) => true;
+}