Update reasoning docs to include API version

[pamelafox]

Purpose

Fixes #2496 by documenting how to set the API version to one that supports the reasoning models.

The other approach is to dynamically default the version in code based on the model selected, but given you already have to use "azd env set" and this is a preview version, I think I prefer the documentation approach.

Also fixes #2495, outdated model names in the documentation.

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[ ] Yes
[X] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by this tutorial
which includes deployment, settings and usage instructions. If text or screenshot need to change in the tutorial,
check the box below and notify the tutorial author. A Microsoft employee can do this for you if you're an external contributor.

[ ] Yes
[X] No

Type of change

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[X] Documentation content changes
[ ] Other... Please describe:

Code quality checklist

See CONTRIBUTING.md for more details.

N/A