Update React Router template for Vite Oxygen workflow

[frandiox]

Summary

• switch templates/react-router dev/build/preview scripts to Vite and React Router
• remove the classic Hydrogen Vite plugin from the template runtime path
• keep @shopify/cli installed for deployment and add an explicit npm run deploy script for shopify hydrogen deploy
• bump Mini Oxygen to 4.2.0 and keep the temporary Hydrogen package export patch for deploy compatibility
• remove deprecated tsconfig baseUrl usage by making the ~ alias path explicit

Notes

• The patch-hydrogen-exports.mjs postinstall shim is still needed for npm installs until the deployment path no longer resolves @shopify/hydrogen/package.json from a package that does not export it.
• We should remove the patch script and postinstall hook after we release the Shopify CLI with the deploy fix.

Testing

• npm ci
• npm run typecheck
• npm run build
• npm run deploy -- --help
• npm run dev -- --host 127.0.0.1 --port 5173, then curl / and confirm SSR content rendered
• npm run preview -- --host 127.0.0.1 --port 4173, then curl / and confirm production SSR content rendered