Add Finder entry in (new) 5.4 migration guide + documentation page

en/appendices/5-4-migration-guide.rst

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+5.4 Migration Guide
+###################
+
+The 5.4.0 release is a backwards compatible with 5.0. It adds new functionality
+and introduces new deprecations. Any functionality deprecated in 5.x will be
+removed in 6.0.0.
+
+Upgrade Tool
+============
+
+The :doc:`upgrade tool </appendices/migration-guides>` provides rector rules for
+automating some of the migration work. Run rector before updating your
+``composer.json`` dependencies::
+
+    bin/cake upgrade rector --rules cakephp54 <path/to/app/src>
+
+Behavior Changes
+================
+
+- WIP
+
+Deprecations
+============
+
+- WIP
+
+New Features
+============
+
+Utility
+-------
+
+- New ``Cake\Utility\Fs\Finder`` class provides a fluent, iterator-based API for
+  discovering files and directories with support for pattern matching, depth
+  control, and custom filters. The ``Cake\Utility\Fs\Path`` class offers
+  cross-platform utilities for path manipulation.