Document all extensions are in maintenance mode

[waylan]

This has been the de facto policy for some time. We are now officially documenting it. Relates to #1612.

Some recommendations for alternative extensions have been included. If anyone would like to include other recommendations, I am open to suggestions.

AI Assistance Disclosure

• No AI tools were used in preparing this PR.
• If AI tools were used, I have disclosed which ones, and fully reviewed and verified their output.

Checklist

• This PR follows the contribution guidelines.
• N/A The code follows the Code Style Guide.
• The commit message follows the Commit Message Style Guide.
• I have added or updated relevant docs, including release notes if applicable which follow the [Documentation Style Guide](Documentation Style Guide).
• N/A I have added or updated relevant tests.
• I have not requested, and will not request, an automated AI review for this PR.

[waylan]

@facelessuser I am waiting for your okay before merging this as the recommendations are all for your extensions. If you have any additional suggestions, we can include them as well.

[facelessuser]

LGTM