Add gradle.properties and .gitignore

gradle.properties sets JVM heap to 2 GiB and enables daemon/parallel/caching
flags — required to prevent Gradle GC thrashing on first build. .gitignore
excludes build outputs, .gradle cache dirs, local.properties, and IDE files
going forward.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gradle.properties

@@ -0,0 +1,7 @@
+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+org.gradle.daemon=true
+org.gradle.parallel=true
+org.gradle.caching=true
+android.useAndroidX=true
+android.enableJetifier=false
+kotlin.code.style=official