chore: exclude generated CHANGELOG.md from Prettier (#40)

release-please generates CHANGELOG.md in a format that does not match the
repo Prettier config, so `prettier --check .` (the Format Check job) fails
on every release PR. The changelog is a generated artifact; add it to
.prettierignore so release PRs pass Format Check.

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

Author: ajGingrich

.prettierignore

@@ -19,3 +19,6 @@ yarn.lock
 
 # Website (has its own formatting)
 website/
+
+# Generated by release-please
+CHANGELOG.md