Move annotations from one domain to another

## Domain change has caused annotations to be lost in context

### Steps to reproduce

1. Direct links to annotations here:

https://hypothes.is/search?q=url%3Ahttps%3A%2F%2Fdlsanthology.commons.mla.org%2Ffrom-reading-to-social-computing%2F

2. Get redirected to a new URL where they cannot be anchored

3. Arriving at this new URL there appear to be no annotations:

https://dlsanthology.mla.hcommons.org/from-reading-to-social-computing/

4. Domain was changed from:

dlsanthology.commons.mla.org

to:

dlsanthology.mla.hcommons.org

### Hoped for behaviour

Existing annotations should anchor at new URL

### Actual behaviour

They do not...

Can they be moved manually?
Can we build something to prevent this common occurrence?

Start by comparing the annotation search results for the old URL with the redirected new URL shown in the issue. Investigate how annotation anchoring handles domain changes and whether manual migration is supported. Done means existing annotations remain discoverable and anchor at the new URL, with a defined approach for preventing or handling future domain changes.

Written by the indexing model from the issue text.