build: drop overbroad **/*.md RAT exclude

The `**/*.md` exclude dropped every markdown file repo-wide from license
checking, not just docs. It was redundant (docs are already covered by
`docs/**`) and overly broad. Removing it; RAT still reports 0 unapproved
because the remaining markdown carries valid headers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: timsaucer

pom.xml

@@ -164,7 +164,6 @@ under the License.
                         <exclude>README.md</exclude>
                         <exclude>CONTRIBUTING.md</exclude>
                         <exclude>docs/**</exclude>
-                        <exclude>**/*.md</exclude>
                         <!-- VCS and editor metadata -->
                         <exclude>.gitignore</exclude>
                         <exclude>.idea/**</exclude>