fix(playground): import @playground/lib (not 'lib') so vite build resolves

Also update the inspection hint in the comment to match the default
`dist/assets/index-<hash>.js` filename now that vite.config.js is gone.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: branchseer

playground/packages/app/src/index.ts

@@ -1,9 +1,9 @@
-import { sum } from 'lib';
+import { sum } from '@playground/lib';
 
 // Vite's `define` plugin substitutes `process.env.NODE_ENV` at build time, so
 // only the branch matching the current NODE_ENV survives dead-code elimination.
-// After `vt run --cache build`, inspect `dist/assets/main.js` to see which
-// literal (`PROD build` or `DEV build`) made it into the bundle.
+// After `vt run --cache build`, inspect `dist/assets/index-<hash>.js` to see
+// which literal (`PROD build` or `DEV build`) made it into the bundle.
 if (process.env.NODE_ENV === 'production') {
   console.log('PROD build:', sum(1, 2, 3));
 } else {