Add build/ directory to .gitignore

The build/ directory contains generated artifacts from rollup and should not be committed to the repository. It is built during the prepublishOnly npm hook.

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

Co-Authored-By: Claude <[email protected]>

Author: claude

.gitignore

@@ -37,6 +37,9 @@ bower_components
 # Compiled binary addons (https://nodejs.org/api/addons.html)
 build/Release
 
+# Build output (generated by rollup)
+build/
+
 # Dependency directories
 node_modules/
 jspm_packages/