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>

.gitignore

@@ -0,0 +1,17 @@
+# Gradle
+.gradle/
+build/
+app/build/
+**/build/
+
+# Local config (not for VCS)
+local.properties
+
+# IDE
+.idea/
+*.iml
+*.iws
+*.ipr
+
+# Android generated
+app/src/main/res/values/generated.xml