Add all 23 GoF design pattern implementations

03-behavioral/chain-of-responsibility/Level2Support.java

@@ -0,0 +1,15 @@
+package chain;
+
+/** Handles MEDIUM priority tickets — technical troubleshooting */
+public class Level2Support extends SupportHandler {
+
+    @Override
+    protected boolean canHandle(SupportTicket ticket) {
+        return ticket.getPriority() == SupportTicket.Priority.MEDIUM;
+    }
+
+    @Override
+    protected void handle(SupportTicket ticket) {
+        System.out.println("  [Level-2] Diagnosed and fixed: " + ticket);
+    }
+}