build: remove deprecated enableJetifier and nonTransitiveRClass flags

Both are deprecated and will be removed in AGP 10.

enableJetifier rewrites old com.android.support artifacts to AndroidX.
The dependency graph contains none, so it was pure build overhead.

nonTransitiveRClass=false made app.intra.R re-export every resource from
every dependency. Turning it off (the modern default) shrinks the R
class and makes resource ownership explicit. Only one reference needed
updating: "up" and "home" in the drawer navigation handler are declared
by AppCompat rather than by this app, so they are now qualified as
androidx.appcompat.R.id. The drawer_menu.xml reference to @id/home is
unaffected, since non-transitive R changes only the generated Java R
classes, not XML resource resolution.

./gradlew clean assembleDebug test passes; lint reports the same five
pre-existing errors as before.

Author: fortuna

Android/app/src/main/java/app/intra/ui/MainActivity.java

@@ -210,7 +210,9 @@ public boolean onNavigationItemSelected(MenuItem item) {
         // Resource IDs are not compile-time constants, so they cannot be used
         // as switch labels.
         final int itemId = item.getItemId();
-        if (itemId == R.id.up || itemId == R.id.home) {
+        // "up" and "home" are declared by AppCompat, not by this app, so with
+        // non-transitive R classes they are not part of app.intra.R.
+        if (itemId == androidx.appcompat.R.id.up || itemId == androidx.appcompat.R.id.home) {
           chooseView(R.id.frame_main);
           return true;
         } else if (itemId == R.id.settings) {

Android/gradle.properties

@@ -19,15 +19,8 @@ org.gradle.jvmargs=-Xmx2048m
 # This option should only be used with decoupled projects. More details, visit
 # http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
 # org.gradle.parallel=true
-android.enableJetifier=true
 android.useAndroidX=true
 
-# Keep legacy AGP behavior after upgrading to AGP 8.
-# TODO: nonTransitiveRClass is deprecated and will be removed in AGP 10.
-# Migrating off it requires auditing every R class reference, so it is left
-# for a separate change.
-android.nonTransitiveRClass=false
-
 ANDROID_COMPILE_SDK_VERSION=36
 ANDROID_BUILD_TOOLS_VERSION=36.0.0