Subresource Integrity

### Code of Conduct

- [x] I agree to follow Django's Code of Conduct

### Feature Description

Now, with DSP taken care of, should we tackle [subresource integrity](https://developer.mozilla.org/en-US/docs/Web/Security/Defenses/Subresource_Integrity) next?

The header is supported by all browsers and might serve as a great addition to Django excellent security suite.

### Problem

With supply chain attacks climbing to [3rd place on the OWASP ranking](https://owasp.org/Top10/2025/), I believe it might be a commendable effort.

Approving CDNs and vendors is a start, but I’d love SHA512 hashes, just in case :wink:

### Request or proposal

proposal

### Additional Details

https://developer.mozilla.org/en-US/docs/Web/Security/Defenses/Subresource_Integrity

### Implementation Suggestions

@RealOrangeOne has been maintaining [django-sri](https://github.com/realOrangeOne/django-sri) for a good while now.

However, his approach was limited by Django's storage system.

I would propose to:

1. The actual header implementation is mostly a copy-paste job of the CSP middleware.
2. Add a `integrity()` function to the `BaseStorage` as well as a sample implementation for the `FileSystemStorage`.
3. Optionally, add an `integrity` template tag to `static`, which doesn't call `url` but the new `integrity` function.
4. Finally, we can safely wrap string paths in media assets in the [Script](https://docs.djangoproject.com/en/5.2/topics/forms/media/#form-media-asset-objects) and `CSS` objects, which render integrity values into the template.