exclude CLAUDE.md from preview changed-files detection

CLAUDE.md files are not rendered by Quarto but match the
docs/**/[^_]*.md pattern, causing false entries in preview
deployment comments.

Author: cderv

.github/workflows/preview.yml

@@ -155,6 +155,8 @@ jobs:
             docs/reference/**/*.json
             docs/cli/*.json
             docs/**/images/*.png
+          files_ignore: |
+            **/CLAUDE.md
           json: true
           escape_json: false