Add all 23 GoF design pattern implementations

02-structural/decorator/PlainTextProcessor.java

@@ -0,0 +1,12 @@
+package decorator;
+/**
+ * Concrete Component — the starting point for decoration.
+ * Returns text unchanged. Decorators wrap around this
+ * and transform the result one layer at a time.
+ */
+public class PlainTextProcessor implements TextProcessor {
+    @Override
+    public String process(String text) {
+        return text;  // no transformation — base case
+    }
+}