Add all 23 GoF design pattern implementations

01-creational/factory-method/PushNotification.java

@@ -0,0 +1,13 @@
+package factorymethod;
+
+public class PushNotification implements Notification {
+
+    @Override
+    public void send(String recipient, String message) {
+        // In production: use Firebase FCM
+        System.out.printf("  [PUSH]  To: %s | Alert: %s%n", recipient, message);
+    }
+
+    @Override
+    public String getType() { return "PUSH"; }
+}