chore: Version 0.9.21, Android-Build-Tooling und Flutter-Abhängigkeiten aktualisiert

- Version auf 0.9.21 angehoben (App und Backend)
- Gradle 8.14.3, AGP 8.11.1, Kotlin 2.2.20; Flutter-Migrator-Flags in gradle.properties
- camera ^0.12.0, mobile_scanner ^7.0.0
- tsconfig ignoreDeprecations auf 5.0, prod.bundle neu gebaut
- upload.sh entfernt

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/android/gradle.properties

@@ -1,3 +1,7 @@
 org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
 android.enableJetifier=true
+# This builtInKotlin flag was added automatically by Flutter migrator
+android.builtInKotlin=false
+# This newDsl flag was added automatically by Flutter migrator
+android.newDsl=false