Feat: Android client Phase 0-3 full implementation

android/.gitignore

@@ -0,0 +1,21 @@
+# Build output
+build/
+app/build/
+
+# Gradle cache and generated configs
+.gradle/
+gradle/gradle-daemon-jvm.properties
+
+# Local config (contains SDK path, machine-specific)
+local.properties
+
+# Android Studio project files
+.idea/
+*.iml
+
+# Signing config
+*.jks
+*.keystore
+
+# Force-track prebuilt static libs (overrides root .gitignore *.a rule)
+!app/src/main/cpp/lib/**/*.a