fix(ci): use relative path for babel preset in babel.config.js

Fix Cypress component tests failing with "Cannot find module '@instructure/ui-babel-preset'".

Issue: Cypress webpack dev server running from its cache directory can't resolve
pnpm workspace packages even with hoisted node linker.

Solution: Use relative path `./packages/ui-babel-preset` instead of package name
in babel.config.js require statement.

This allows babel to directly require the workspace package regardless of pnpm's
module resolution strategy.

Fixes: Cypress component tests and visual regression tests

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

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

Author: balzss

babel.config.js

@@ -25,7 +25,7 @@
 module.exports = {
   presets: [
     [
-      require('@instructure/ui-babel-preset'),
+      require('./packages/ui-babel-preset'),
       {
         coverage: Boolean(process.env.COVERAGE),
         esModules: Boolean(process.env.ES_MODULES),