chore: Update .gitignore to include blog-posts directory and exclude EPUB files

- Added blog-posts/ to .gitignore to prevent tracking of blog-related files.
- Included rule to ignore all EPUB files in the root directory for cleaner repository management.

.gitignore

@@ -46,3 +46,6 @@ yarn-error.log*
 # Keep .claude/ clean for hand-on section
 .claude/
 blog-posts/
+
+# EPUB files in root directory
+/*.epub