Add local copy of mailchimp assets.

[freakboy3742]

Uses local copies of the Mailchimp assets, rather than a CDN copy, to possibly avoid CORB issues.

Fixes #607.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[github-actions]

Visit the preview URL for this PR (updated for commit a4b5865):

https://beeware-org--pr608-mailchimp-local-wqydbktl.web.app

_{(expires Fri, 11 Apr 2025 04:10:24 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

_{Sign: b0da44bc067e7d9a4255c77cb2c5fce572218cec}

[freakboy3742]

@danyeaw This is an experiment to see if local assets fix the problem you were seeing. We can't reproduce post-json, which is the page that was giving you the CORB error - that appears to be a dynamic page, not a CDN-served asset.

Also - the preview URL isn't hosted in quite the same way as the production site, so this isn't a completely reliable test; but if you can subscribe using this URL:

https://beeware-org--pr608-mailchimp-local-wqydbktl.web.app/community/keep-informed/

it's definitely a positive sign. If it does work, the thing to check will be whether the preview site works generally - for example, does subscription work if you visit this url:

https://beeware-org--pr606-2025q2-tj4nn6bz.web.app/community/keep-informed/

That's the preview of #606, so it isn't using the local Mailchimp assets, but it is using the preview domain (which is a Google Cloud deployment). That will isolate whether it's being served by Github Pages that is the underlying issue.

[danyeaw]

This PR is working:

and so is PR606:

[freakboy3742]

The fact that the older preview works suggests it's an issue with GitHub pages (or the CDN, or the node of the CDN that you're connected to)... but I have no idea how to fix that, short of not using form embedding...

[freakboy3742]

Closing on the basis that it seems unlikely that it will solve the problem.