"Visit annotations in context" links broken for non-public domains

### Steps to reproduce
1. Install hypothesis script on a non-public domain (i.e. localhost or an on-prem network)
2. Create a new annotation
3. On your profile on hypothes.is, tap **Visit annotations in context**

### Expected behaviour
I am taken to the link

### Actual behaviour
I'm taken to a _web viewer_ of that link on hypothes.is, which cannot load the domain

### Additional details
I'd love to be able to use this for internal tools and non-publicly-accessible pages, but the limitations which assume URLs are public and universal hurt the ability to do so. Right now, most everything works great for an on-prem site, except for comment links in emails (from replies) and links from the hypothes.is site.

No files or tests are named in the issue. Reproduce the profile's “Visit annotations in context” flow with a localhost or on-prem annotation, then trace the web viewer redirect and compare it with the expected direct link behavior; done means non-public links open in their original context without relying on hypothes.is access.

Written by the indexing model from the issue text.