fix: update gitignore to follow Panda CSS best practices

Change from specific file exclusions to exclude entire styled-system directory.
This aligns with Panda CSS recommendations to treat generated files as build output.

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

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

.gitignore

@@ -8,10 +8,7 @@ dist/
 *.tsbuildinfo
 
 # Generated CSS (Panda CSS / styled-system)
-**/styled-system/styles.css
-**/styled-system/chunks/
-**/styled-system/global.css
-**/styled-system/reset.css
+**/styled-system/
 
 # Environment
 .env*