Add mobile/.gitignore (should have been in prior cleanup commit)

mobile/.gitignore

@@ -0,0 +1,36 @@
+# Node / npm — keep package-lock.json for reproducible CI builds,
+# ignore only the installed tree.
+node_modules/
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Capacitor generated files (rewritten by `npx cap sync`)
+# Keep the *project* (mobile/android/, mobile/ios/) but not the
+# per-sync mirrors.
+android/app/src/main/assets/public/
+android/app/src/main/assets/capacitor.config.json
+android/app/src/main/assets/capacitor.plugins.json
+android/app/capacitor.build.gradle
+android/capacitor.settings.gradle
+android/capacitor-cordova-android-plugins/
+
+ios/App/App/public/
+ios/App/capacitor-cordova-ios-plugins/
+ios/App/Pods/
+ios/App/Podfile.lock
+
+# Android build outputs & local state
+android/.gradle/
+android/build/
+android/app/build/
+android/app/release/
+android/local.properties
+android/app/release/output-metadata.json
+android/.idea/
+*.apk
+*.aab
+*.jks
+
+# macOS
+.DS_Store