Build Android release APK; fix release build and bump sentry_flutter

Two build-blocking issues fixed to get a release APK building at all:

- flutter_local_notifications (V3-06) requires core library desugaring below API 33; enabled it and added the desugar_jdk_libs dependency.
- sentry_flutter 8.14.2's bundled Kotlin plugin declares languageVersion 1.6, incompatible with this project's Kotlin 2.4.0 toolchain. Bumped to sentry_flutter ^9.0.0 (resolved 9.27.0), which builds clean; left three copyWith deprecation infos from the v9 API as a follow-up, not blocking.

Signed with the debug keystore (release signingConfig still points at debug -- no release signing config exists yet, matches the existing TODO in build.gradle.kts). app-release.apk committed directly (68.7MB, force-added past .gitignore's build/ exclusion) per request, so it can be pushed once a remote exists.

android/app/build.gradle.kts

@@ -12,6 +12,8 @@ android {
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
+        // flutter_local_notifications (V3-06) requires this on API levels below 33.
+        isCoreLibraryDesugaringEnabled = true
     }
 
     defaultConfig {
@@ -44,6 +46,10 @@ kotlin {
     }
 }
 
+dependencies {
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.1.4")
+}
+
 flutter {
     source = "../.."
 }