Add release signing configuration and keystore.

The `build.gradle.kts` file is updated to include a release signing configuration that uses environment variables for passwords and references a new `keystore.jks` file. Minification is enabled for release builds.

Author: halifox

app/build.gradle.kts

@@ -23,11 +23,22 @@ android {
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }
-
+    signingConfigs {
+        create("release") {
+            keyAlias = "release"
+            keyPassword = System.getenv("KEY_PASSWORD")
+            storeFile = file("../keystore.jks")
+            storePassword = System.getenv("STORE_PASSWORD")
+        }
+    }
     buildTypes {
         release {
-            isMinifyEnabled = false
-            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+            isMinifyEnabled = true
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+            signingConfig = signingConfigs.getByName("release")
         }
     }
     compileOptions {