chore(platform): assets app + config Android/iOS + screenshots

- Icônes app (hdpi/mdpi/xhdpi/xxhdpi/xxxhdpi + iOS AppIcon) régénérées
- Launch screens Android + iOS actualisés
- ios/Runner : Info.plist, LaunchScreen.storyboard, project.pbxproj
- android/gradle.properties, drawables, styles (values + values-night)
- assets/images : branding/logo
- Screenshots Flutter (flutter_01-04.png) + script PowerShell start-emulators

android/gradle.properties

@@ -1,4 +1,6 @@
 org.gradle.jvmargs=-Xmx4G -XX:MaxMetaspaceSize=2G -XX:+HeapDumpOnOutOfMemoryError -Djava.net.preferIPv4Stack=true
+org.gradle.parallel=false
+org.gradle.workers.max=1
 android.useAndroidX=true
 android.enableJetifier=true