chore(hw-03): initialize gradle java project with design patterns structure

hw-03/project-root/app/build.gradle.kts

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+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Java application project to get you started.
+ * For more details on building Java & JVM projects, please refer to https://docs.gradle.org/9.6.1/userguide/building_java_projects.html in the Gradle documentation.
+ * This project uses @Incubating APIs which are subject to change.
+ */
+
+plugins {
+    // Apply the application plugin to add support for building a CLI application in Java.
+    application
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+    // This dependency is used by the application.
+    implementation(libs.guava)
+}
+
+testing {
+    suites {
+        // Configure the built-in test suite
+        val test = named<JvmTestSuite>("test") {
+            // Use JUnit Jupiter test framework
+            useJUnitJupiter("6.0.1")
+        }
+    }
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+application {
+    // Define the main class for the application.
+    mainClass = "org.example.App"
+}