feat: implement Android app signing setup and update .gitignore for keystore files

android/keystore.properties.example

@@ -0,0 +1,14 @@
+# Copy this file to keystore.properties and fill in your actual values
+# NEVER commit keystore.properties to git!
+
+# Path to your keystore file (relative to android/ directory)
+storeFile=paarrot-release.keystore
+
+# Keystore password
+storePassword=your_keystore_password_here
+
+# Key alias
+keyAlias=paarrot
+
+# Key password
+keyPassword=your_key_password_here