feat: 안드로이드 하이브리드 앱(Capacitor) 구성

- capacitor.config + android/ 네이티브 프로젝트
- 앱 전용 빌드(.env.capacitor, build:app), 뒤로가기·safe-area
- docs/ANDROID.md

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

android/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.3-all.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists