Broken redirects and internal link point to missing /apps/quickstart/create-new-app page

## Summary

Several redirects and at least one internal documentation link point to `/apps/quickstart/create-new-app`, but this route does not appear to exist in the current docs source and returns 404 on the live docs site.

## What I found

The following URL returns 404:

https://docs.base.org/apps/quickstart/create-new-app

However, multiple references in the docs point to this missing route.

Examples in [docs/docs.json](cci:7://file:///C:/Users/Zeki/CascadeProjects/base-docs-research/docs/docs.json:0:0-0:0):

- `docs/docs.json:1785`
- `docs/docs.json:2149`
- `docs/docs.json:2153`
- `docs/docs.json:2157`
- `docs/docs.json:2161`

There is also an internal link in:

- `docs/get-started/learning-resources.mdx:21`

The link is:

`[Apps](/apps/quickstart/create-new-app)`

## Expected behavior

Redirects and internal links should point to an existing Apps quickstart page.

## Actual behavior

The route `/apps/quickstart/create-new-app` does not exist and returns 404.

## Suggested fix

Update the references to the existing Apps quickstart page:

`/apps/quickstart/build-app`

This seems to be the current correct route because:

- [docs/apps/quickstart/build-app.mdx](cci:7://file:///C:/Users/Zeki/CascadeProjects/base-docs-research/docs/apps/quickstart/build-app.mdx:0:0-0:0) exists
- [docs/docs.json](cci:7://file:///C:/Users/Zeki/CascadeProjects/base-docs-research/docs/docs.json:0:0-0:0) lists `apps/quickstart/build-app` under the Apps > Quickstart navigation
- The `/quickstart` redirect already points to `/apps/quickstart/build-app`

## Impact

Users coming from migrated Mini Apps or Cookbook URLs may land on a 404 page. The Learning Resources page also links users to a missing Apps page.