[WIP] API docs changes for RR7

[rorytanner]

This PR accompanies https://github.com/Shopify/shopify-dev/pull/57281 with changes to the Hydrogen API reference (mainly updating package names to react-router!)

Still a few loose ends, but this should be mostly there. cc @balazsbajorics @blittle

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset.
If the changes are user-facing and should cause a version bump, run npm run changeset add to track your changes and include them in the next release CHANGELOG.
If you are making simple updates to examples or documentation, you do not need to add a changeset.

[shopify]

Oxygen deployed a preview of your remix-rr-api-docs branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	May 20, 2025 3:04 PM
metaobjects	✅ Successful (Logs)	Preview deployment	Inspect deployment	May 20, 2025 3:04 PM
custom-cart-method	✅ Successful (Logs)	Preview deployment	Inspect deployment	May 20, 2025 3:04 PM
classic-remix	✅ Successful (Logs)	Preview deployment	Inspect deployment	May 14, 2025 2:46 PM
third-party-queries-caching	✅ Successful (Logs)	Preview deployment	Inspect deployment	May 20, 2025 3:04 PM

Learn more about Hydrogen's GitHub integration.

[blittle]

I think this is probably good?

[rorytanner]

closing this in favour of #2947 because rebase