feat(canvas): 배경 투명도 조절 및 시네마틱 번역 추가

- AsciiCanvasPainter/Widget에 backgroundOpacity 파라미터 추가
- 기본값 0.5 (50% 투명도)로 배경 렌더링
- CinematicView 텍스트에 l10n 번역 적용

lib/src/core/animation/canvas/ascii_canvas_painter.dart

@@ -43,6 +43,7 @@ class AsciiCanvasPainter extends CustomPainter {
     this.gridWidth = 60,
     this.gridHeight = 8,
     this.backgroundColor = AsciiColors.background,
+    this.backgroundOpacity = 0.5,
     this.layerVersion = 0,
   });
 
@@ -58,6 +59,9 @@ class AsciiCanvasPainter extends CustomPainter {
   /// 배경색
   final Color backgroundColor;
 
+  /// 배경 투명도 (0.0 ~ 1.0, 기본값 0.5 = 50%)
+  final double backgroundOpacity;
+
   /// 레이어 버전 (변경 감지용)
   final int layerVersion;
 
@@ -83,10 +87,10 @@ class AsciiCanvasPainter extends CustomPainter {
       _lastFontSize = fontSize;
     }
 
-    // 2. 배경 채우기
+    // 2. 배경 채우기 (투명도 적용)
     canvas.drawRect(
       Rect.fromLTWH(0, 0, size.width, size.height),
-      Paint()..color = backgroundColor,
+      Paint()..color = backgroundColor.withValues(alpha: backgroundOpacity),
     );
 
     // 3. 레이어별 렌더링 (z-order 순)

lib/src/core/animation/canvas/ascii_canvas_widget.dart

@@ -13,6 +13,7 @@ class AsciiCanvasWidget extends StatelessWidget {
     required this.layers,
     this.gridWidth = 60,
     this.gridHeight = 8,
+    this.backgroundOpacity = 0.5,
     this.isAnimating = true,
     this.layerVersion = 0,
   });
@@ -26,6 +27,9 @@ class AsciiCanvasWidget extends StatelessWidget {
   /// 그리드 높이 (행 수)
   final int gridHeight;
 
+  /// 배경 투명도 (0.0 ~ 1.0, 기본값 0.5 = 50%)
+  final double backgroundOpacity;
+
   /// 애니메이션 활성 상태 (willChange 최적화용)
   final bool isAnimating;
 
@@ -40,6 +44,7 @@ class AsciiCanvasWidget extends StatelessWidget {
           layers: layers,
           gridWidth: gridWidth,
           gridHeight: gridHeight,
+          backgroundOpacity: backgroundOpacity,
           layerVersion: layerVersion,
         ),
         size: Size.infinite,