Remove redundant default export from vite plugin

The default export alongside the named export caused
"Importing binding name 'default' cannot be resolved by star export entries"
when consumers re-exported with `export *`.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mattlenz

src/vite/index.ts

@@ -404,5 +404,3 @@ export function kb(userConfig?: KbConfig): Plugin[] {
 
   return [kbContent, kbBuild];
 }
-
-export default kb;