Update demo entries in demos.yaml

[mit-mit]

Removed several demo entries and added a new demo for 'Wonderous'.

Description of what this PR is changing or adding, and why:

Issues fixed by this PR (if any):

PRs or commits this PR depends on (if any):

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks
  of 80 characters or fewer.

[gemini-code-assist]

Code Review

This pull request replaces several older Flutter demo entries in demos.yaml with a new entry for the Wondrous app. The reviewer identified spelling and casing errors in the new entry, such as 'Wonderous' instead of 'Wondrous' and 'MacOS' instead of 'macOS', and provided a corrected configuration block.

[abdallahshaban557]

Just waiting for the preview link and then will approve!

[flutter-website-bot]

Staged preview of the updated docs.flutter.dev site (updated for commit 8b62c40):

https://flutter-docs-prod--docs-pr13476-mit-mit-patch-1-g23rmb5u.web.app

[flutter-website-bot]

Staged preview of the updated flutter.dev site (updated for commit 8b62c40):

https://flutter-dev-230821--www-pr13476-mit-mit-patch-1-omsayau8.web.app

[mit-mit]

https://flutter-dev-230821--www-pr13476-mit-mit-patch-1-omsayau8.web.app/showcase

@abdallahshaban557

[sfshaza2]

lgtm, but won't land in case @abdallahshaban557 has feedback.

[abdallahshaban557]

LGTM