Fix flutter project with new android-studio version:

- upgrade gradle from 7.5 to 7.6.1
  - change java target from 1.8 to 17
  - set flutter jdk-dir to system-jdk (instead of now-incompatible android-studio bundled jdk)
    (android studio bundles jdk 21, jdk 21 needs gradle 8.4, flutetr does not work with gradle > 7.6.1 )
    => see https://docs.gradle.org/current/userguide/compatibility.html#java
    =>     https://www.liquidbcn.com/en/insights/solving-issues-android-studio-ladybug-java-21-flutter

flutter/Makefile

@@ -1,14 +1,22 @@
 
 
+# Setup
+#
+# flutter config --jdk-dir "/usr/lib/jvm/default-runtime/bin"
+# sudo archlinux-java set java-17-openjdk
+#
+
+
+
 run:
 	flutter pub run build_runner build
-	flutter run
+	_JAVA_OPTIONS="" flutter run
 	
 run-android:
 	ping -c1 10.10.10.177
 	adb connect 10.10.10.177:5555
 	flutter pub run build_runner build
-	flutter run -d 10.10.10.177:5555
+	_JAVA_OPTIONS="" flutter run -d 10.10.10.177:5555
 	
 test:
 	dart analyze
@@ -24,4 +32,8 @@ autoreload:
 	@_utils/autoreload.sh
 	
 icons:
-	flutter pub run flutter_launcher_icons -f "flutter_launcher_icons.yaml"
+	flutter pub run flutter_launcher_icons -f "flutter_launcher_icons.yaml"
+
+clean:
+	cd android && ./gradlew clean
+	flutter clean