Add Android signing configuration to Gradle

- Configure signingConfigs to read from environment variables
- Apply signing to release builds when keystore is available
- Support both signed and unsigned builds

src-tauri/gen/android/app/build.gradle.kts

@@ -24,6 +24,23 @@ android {
         versionCode = tauriProperties.getProperty("tauri.android.versionCode", "1").toInt()
         versionName = tauriProperties.getProperty("tauri.android.versionName", "1.0")
     }
+
+    signingConfigs {
+        create("release") {
+            val keystorePath = System.getenv("ANDROID_KEYSTORE_PATH")
+            val keystorePassword = System.getenv("ANDROID_KEYSTORE_PASSWORD")
+            val keyAlias = System.getenv("ANDROID_KEY_ALIAS")
+            val keyPassword = System.getenv("ANDROID_KEY_PASSWORD")
+
+            if (keystorePath != null && keystorePassword != null && keyAlias != null && keyPassword != null) {
+                storeFile = file(keystorePath)
+                storePassword = keystorePassword
+                this.keyAlias = keyAlias
+                this.keyPassword = keyPassword
+            }
+        }
+    }
+
     buildTypes {
         getByName("debug") {
             manifestPlaceholders["usesCleartextTraffic"] = "true"
@@ -43,6 +60,12 @@ android {
                     .plus(getDefaultProguardFile("proguard-android-optimize.txt"))
                     .toList().toTypedArray()
             )
+
+            // Sign with release config if available
+            val releaseSigningConfig = signingConfigs.getByName("release")
+            if (releaseSigningConfig.storeFile != null) {
+                signingConfig = releaseSigningConfig
+            }
         }
     }
     kotlinOptions {