fix: tanstack docs errors

[MattieTK]

Summary

There's a few silly mistakes in the TanStack Start docs (that were my fault) that this PR fixes. Thanks @jamesopstad!

It also tidies up the createServerEntry implementation which right now doesn't add enough to be worth mentioning.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/workers/	@cloudflare/workers-docs, @GregBrimble, @irvinebroque, @mikenomitch, @korinne, @WalshyDev, @cloudflare/deploy-config, @cloudflare/pcx-technical-writing, @cloudflare/wrangler, @mattietk

[github-actions]

Preview URL: https://ec2e27b2.preview.developers.cloudflare.com
Preview Branch URL: https://mattietk-tanstack-docs-fix.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/workers/framework-guides/web-apps/tanstack-start/	https://mattietk-tanstack-docs-fix.preview.developers.cloudflare.com/workers/framework-guides/web-apps/tanstack-start/