Follow-up: Exercise Rspack 2 switcher path in tutorial

[justin808]

Follow-up: Exercise Rspack 2 switcher path in tutorial

Source PR: #771

Why

PR #771 updates the dormant Rspack dependency family for Shakapacker 10.2.0 (@rspack/cli / @rspack/core 2.0.4 and @rspack/plugin-react-refresh 2.0.0). The app currently runs with assets_bundler: webpack, so the normal CI and system specs exercise the webpack path, not the TODO path that switches the tutorial back to Rspack.

Expected follow-up evidence

• Switch the tutorial to the documented Rspack path when the blocking RSC issue is ready.
• Run an actual Rspack build and dev/HMR smoke, not only a constructor/import probe.
• Confirm @rspack/core 2.x, @rspack/cli 2.x, and @rspack/plugin-react-refresh 2.x work together in this tutorial.
• Record whether any additional config changes are needed before enabling the Rspack path for users.

Current PR evidence

• Webpack path: bin/conductor-exec yarn build:test passes.
• Dev-server/HMR path currently exercised by bin/shakapacker-dev-server is webpack because assets_bundler: webpack.
• Rspack dependency compatibility in PR Update Shakapacker to 10.2.0 #771 was limited to a direct plugin construction probe.

Non-goal

This issue does not block landing the Shakapacker 10.2.0 dependency update while the tutorial remains on webpack.