UXarray should have an AI Usage Disclosure (and maybe a Policy)

[erogluorhan]

Originally posted by @Sevans711 in #1613

1. UXarray should add an AI Usage Disclosure section to the default github PR form template? (See also some recent work to improve that form: clean up github PR form template #1608)

2. Maybe the repo should have a lightweight AI Usage Policy as well? If we go this route, it can be linked to from within the above PR checklist section.

There are many good examples online already, and the original discussion seemed to lean towards a lightweight beginning to this, e.g. something in between what holoview and xarray do, but it can be anything else that is a ligthweight start that can be improved over time.

Example: holoviews

holoviews PR form includes the following:

## AI Disclosure
<!-- Delete this section if AI was not used, else specify the tool/model
    (e.g. Cursor + Sonnet 4.6, Claude Code + Opus 4.6, ChatGPT) and briefly describe how it was used.
    Failure to disclose AI usage may result in a ban. -->

Tool & Model:
Usage:

- [ ] I have tested all AI-generated content in my PR.
- [ ] I take responsibility for all AI-generated content in my PR.

Example: xarray

xarray added an AI usage policy a few months ago (pydata/xarray#11126), as well as a section on the PR form:

### AI Disclosure

<!--- Please review our AI & contribution guidelines: https://docs.xarray.dev/en/stable/contribute/ai-policy.html.
    Remove this section if your PR does not contain AI-generated content. --->

- [ ] This PR contains AI-generated content.
  - [ ] I have tested any AI-generated content in my PR.
  - [ ] I take responsibility for any AI-generated content in my PR.
    <!--- If you used AI to generate code, please specify the tool used and the prompt below. --->
    Tools: {e.g., Claude, Codex, GitHub Copilot, ChatGPT, etc.}

[Sevans711]

I'd be happy to take this one! It is "blocked" (sort of…) by work on #1608. I would suggest either:

1. Delay starting this until 1608 merges.
2. Add a lightweight AI disclosure section to the PR form as part of 1608 (in the spirit of @rajeeja's comment in discussion AI Usage Policy / AI Usage Dislosure? #1613). But, leave this issue open for a longer-term discussion/consideration of what the uxarray community wants from an AI usage policy.

I may have a slight preference for (2). Do you have a preference on this, @erogluorhan?