feat: Windows build support + title bar tamamen saydam

lib/widgets/custom_title_bar.dart

@@ -15,19 +15,8 @@ class CustomTitleBar extends StatelessWidget {
           height: 40,
           child: Stack(
             children: [
-              Positioned.fill(
-                child: Container(
-                  decoration: BoxDecoration(
-                    gradient: LinearGradient(
-                      begin: Alignment.topCenter,
-                      end: Alignment.bottomCenter,
-                      colors: [
-                        Colors.black.withValues(alpha: 0.6),
-                        Colors.black.withValues(alpha: 0.0),
-                      ],
-                    ),
-                  ),
-                ),
+              const Positioned.fill(
+                child: SizedBox.shrink(),
               ),
               Positioned(
                 right: 0,