feat(mobile-app): auto-increment version code on each build

- Add version.properties file to track build number locally
- Auto-increment versionCode on every debug/release build
- Version name format: major.minor.patch.buildNumber (e.g., 1.0.0.123)
- Add version.properties to .gitignore (each developer has own build number)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/mobile-app/.gitignore

@@ -44,6 +44,9 @@ app.*.map.json
 /android/app/profile
 /android/app/release
 
+# Auto-generated version file (each developer has their own build number)
+/android/app/version.properties
+
 # Release signing keys (IMPORTANT: never commit these!)
 /publish/
 *.keystore

frontend/mobile-app/android/app/build.gradle.kts

@@ -1,5 +1,6 @@
 import java.util.Properties
 import java.io.FileInputStream
+import java.io.FileOutputStream
 
 plugins {
     id("com.android.application")
@@ -15,6 +16,33 @@ if (keyPropertiesFile.exists()) {
     keyProperties.load(FileInputStream(keyPropertiesFile))
 }
 
+// ============================================
+// Auto-increment version code on each build
+// ============================================
+val versionPropertiesFile = rootProject.file("app/version.properties")
+val versionProperties = Properties()
+
+fun getAutoVersionCode(): Int {
+    if (versionPropertiesFile.exists()) {
+        versionProperties.load(FileInputStream(versionPropertiesFile))
+    }
+    val currentCode = versionProperties.getProperty("VERSION_CODE", "0").toInt()
+    val newCode = currentCode + 1
+    versionProperties.setProperty("VERSION_CODE", newCode.toString())
+    versionProperties.store(FileOutputStream(versionPropertiesFile), "Auto-generated version code - DO NOT EDIT MANUALLY")
+    return newCode
+}
+
+// Get auto-incremented version code
+val autoVersionCode = getAutoVersionCode()
+
+// Version name format: major.minor.patch (from pubspec.yaml) + build number
+// Example: 1.0.0.123
+fun getAutoVersionName(): String {
+    val flutterVersionName = flutter.versionName ?: "1.0.0"
+    return "$flutterVersionName.$autoVersionCode"
+}
+
 android {
     namespace = "com.rwadurian.rwa_android_app"
     compileSdk = flutter.compileSdkVersion
@@ -36,8 +64,9 @@ android {
         // For more information, see: https://flutter.dev/to/review-gradle-config.
         minSdk = flutter.minSdkVersion
         targetSdk = flutter.targetSdkVersion
-        versionCode = flutter.versionCode
+        // Auto-incremented version code and name
-        versionName = flutter.versionName
+        versionCode = autoVersionCode
+        versionName = getAutoVersionName()
     }
 
     signingConfigs {