docs(js): Update Hydrogen with React Router quick start guide (#16535)

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## DESCRIBE YOUR PR
This branch contains the updated quick start guide for Hydrogen with
React Router (Oxygen/Cloudflare).

What I did:
- updated structure and flow to be in line with our quick start guide
template
- added missing content such as Verify, Next, steps, onboarding options
(took content from React router guide)

## IS YOUR CHANGE URGENT?  

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- [ ] Urgent deadline (GA date, etc.): <!-- ENTER DATE HERE -->
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- [x] None: Not urgent, can wait up to 1 week+

## SLA

- Teamwork makes the dream work, so please add a reviewer to your PRs.
- Please give the docs team up to 1 week to review your PR unless you've
added an urgent due date to it.
Thanks in advance for your help!

## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [ ] Checked Vercel preview for correctness, including links
- [ ] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
- [ ] PR was reviewed and approved by a member of the [Sentry docs
team](https://github.com/orgs/getsentry/teams/docs)

## EXTRA RESOURCES

- [Sentry Docs contributor guide](https://docs.sentry.io/contributing/)

Author: inventarSarah