chore: Add book build outputs to gitignore

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: silversurfer562

.gitignore

@@ -97,3 +97,7 @@ server.json
 
 # Embedded git repositories
 10_9_2025_ai_nurse_florence/
+
+# Generated book files
+dist/empathy-book.*
+ebook-site/