Add all 23 GoF design pattern implementations (2026-06-13)

02-structural/decorator/TextProcessor.java

@@ -0,0 +1,10 @@
+package decorator;
+
+/**
+ * Component interface — defines what all text processors do.
+ * Both the concrete processor AND all decorators implement this.
+ * This is what makes them stackable.
+ */
+public interface TextProcessor {
+    String process(String text);
+}