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/ios/Flutter/Generated.xcconfig

@@ -0,0 +1,14 @@
+// This is a generated file; do not edit or check into version control.
+FLUTTER_ROOT=/opt/flutter
+FLUTTER_APPLICATION_PATH=/root/JustAMessenger/client
+COCOAPODS_PARALLEL_CODE_SIGN=true
+FLUTTER_TARGET=lib/main.dart
+FLUTTER_BUILD_DIR=build
+FLUTTER_BUILD_NAME=1.0.0
+FLUTTER_BUILD_NUMBER=1
+EXCLUDED_ARCHS[sdk=iphonesimulator*]=i386
+EXCLUDED_ARCHS[sdk=iphoneos*]=armv7
+DART_OBFUSCATION=false
+TRACK_WIDGET_CREATION=true
+TREE_SHAKE_ICONS=false
+PACKAGE_CONFIG=.dart_tool/package_config.json