Fix Studio contributor README links and Node version note (#47571)

## I have read the
[CONTRIBUTING.md](https://github.com/supabase/supabase/blob/master/CONTRIBUTING.md)
file.

YES

## What kind of change does this PR introduce?

docs update

## Description

- Replace the broken checklist link in apps/studio/README.md with the
main contributing guide.
- Update the Studio setup note in apps/studio/README.md to match the
repo Node pin in .nvmrc.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Updated the contribution instructions to point to the main
contributing guide.
* Bumped the recommended Node.js version in the developer quickstart
from v20 to v22.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/studio/README.md

@@ -28,7 +28,7 @@ Project settings are managed outside of the Dashboard. If you use docker compose
     - Type: `chore | fix | feature`
     - The branch name is arbitrary — just make sure it summarizes the work.
 - When you send a PR to `master`, it will automatically tag members of the frontend team for review.
-- Review the [contributing checklists](contributing/contributing-checklists.md) to help test your feature before sending a PR.
+- Review the main [contributing guide](../../CONTRIBUTING.md) to help test your feature before sending a PR.
 - The Dashboard is under active development. You should run `git pull` frequently to make sure you're up to date.
 
 ### Developer Quickstart
@@ -37,7 +37,7 @@ Project settings are managed outside of the Dashboard. If you use docker compose
 > **Supabase internal use:** To develop on Studio locally with the backend services, see the instructions in the [internal `infrastructure` repo](https://github.com/supabase/platform/blob/develop/docs/contributing.md).
 
 ```bash
-# You'll need to be on Node v20
+# You'll need to be on Node v22
 # in /studio
 
 ## For external contributors