сборка: APK (Android) + Linux Desktop

- Исправлены ошибки Flutter анализа (withOpacity, pbkdf2, импорты)
- Упрощён pubspec.yaml (только нужные зависимости)
- Android APK собран: build/app/outputs/flutter-apk/app-release.apk (22MB)
- Linux Desktop собран: build/linux/x64/release/bundle/jam_client

Для Windows: кросс-компиляция невозможна с Linux.
Нужен Windows хост для flutter build windows.

client/lib/widgets/message_bubble.dart

@@ -39,7 +39,7 @@ class MessageBubble extends StatelessWidget {
                       width: 32,
                       height: 32,
                       decoration: BoxDecoration(
-                        color: ThemeService.primary.withValues(alpha: 0.8),
+                        color: ThemeService.primary.withOpacity(0.8),
                         borderRadius: BorderRadius.circular(16),
                       ),
                       child: Center(
@@ -88,7 +88,7 @@ class MessageBubble extends StatelessWidget {
                           borderRadius: BorderRadius.circular(4),
                           border: Border(
                             left: BorderSide(
-                              color: ThemeService.primary.withValues(alpha: 0.5),
+                              color: ThemeService.primary.withOpacity(0.5),
                               width: 3,
                             ),
                           ),
@@ -154,7 +154,7 @@ class MessageBubble extends StatelessWidget {
             width: 120,
             height: 4,
             decoration: BoxDecoration(
-              color: ThemeService.textMuted.withValues(alpha: 0.3),
+              color: ThemeService.textMuted.withOpacity(0.3),
               borderRadius: BorderRadius.circular(2),
             ),
           ),