feat: Enhance Android release signing process and add verification script

android/app/build.gradle.kts

@@ -1,3 +1,6 @@
+import java.io.FileInputStream
+import java.util.Properties
+
 plugins {
     id("com.android.application")
     id("kotlin-android")
@@ -6,6 +9,15 @@ plugins {
     id("com.google.gms.google-services")
 }
 
+val keystoreProperties = Properties()
+val keystorePropertiesFile = rootProject.file("key.properties")
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(FileInputStream(keystorePropertiesFile))
+}
+
+val releaseStoreFile = keystoreProperties.getProperty("storeFile")
+val hasReleaseSigning = !releaseStoreFile.isNullOrBlank()
+
 android {
     namespace = "com.example.reader_app"
     compileSdk = flutter.compileSdkVersion
@@ -31,11 +43,25 @@ android {
         versionName = flutter.versionName
     }
 
+    signingConfigs {
+        if (hasReleaseSigning) {
+            create("release") {
+                storeFile = file(releaseStoreFile!!)
+                storePassword = keystoreProperties.getProperty("storePassword")
+                keyAlias = keystoreProperties.getProperty("keyAlias")
+                keyPassword = keystoreProperties.getProperty("keyPassword")
+            }
+        }
+    }
+
     buildTypes {
         release {
-            // TODO: Add your own signing config for the release build.
-            // Signing with the debug keys for now, so `flutter run --release` works.
-            signingConfig = signingConfigs.getByName("debug")
+            // Use release keystore when available; fallback to debug for local dev builds.
+            signingConfig = if (hasReleaseSigning) {
+                signingConfigs.getByName("release")
+            } else {
+                signingConfigs.getByName("debug")
+            }
         }
     }
 }