Fix DecoratedEventMap to handle split $decorator path navigation

Values.get() splits "$decorator.field" into ["$decorator", "field"]
segments, but DecoratedEventMap.get() only matched the "$decorator."
prefix. Return the first decorator map for the bare "$decorator" key.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jbachorik

jfr-shell-core/src/main/java/io/jafar/shell/jfrpath/JfrPathEvaluator.java

@@ -2459,6 +2459,12 @@ private static class DecoratedEventMap extends java.util.AbstractMap<String, Obj
     public Object get(Object key) {
       String keyStr = String.valueOf(key);
 
+      // Handle bare "$decorator" key (from path navigation: "$decorator" / "field")
+      if ("$decorator".equals(keyStr)) {
+        if (decorators.isEmpty()) return null;
+        return decorators.get(0);
+      }
+
       // Check if accessing decorator field
       if (keyStr.startsWith(DECORATOR_PREFIX)) {
         String decoratorField = keyStr.substring(DECORATOR_PREFIX.length());