Pin version of shadcn, fixes #309

[JCB-K]

The latest version of the UI package does not include the CLI anymore, it's published under shadcn now - this PR fixes that by pinning the version to 0.8.0, the latest previous version that works.

It would be nice to start using the new CLI, but it's incompatible with the current setup inside NX: it expects package.json and components.json to be defined within the same directory. I think the better approach would be to implement a NX-specific version of the add command instead of using the upstream CLI - it's not particularly complex.

[nx-cloud]

☁️ Nx Cloud Report

CI is running/has finished running commands for commit c940745. As they complete they will appear below. Click to see the status, the terminal output, and the build insights.

📂 See all runs for this CI Pipeline Execution

---

✅ Successfully ran 7 targets

• nx run-many --target=e2e --projects=shadcn-ui-e2e --output-style=stream
• nx run-many --target=test --projects=shadcn-ui --output-style=stream --parallel=4
• nx compile actions-run-many
• nx run-many --target=build --projects=shadcn-ui --output-style=stream --prod
• nx compile actions-set-shas
• nx run-many --target=version --projects=shadcn-ui --output-style=stream
• nx compile actions-plan

---

Sent with 💌 from NxCloud.