HTTP 5xx error when viewing high page numbers in search results

### Steps to reproduce

1. Go to https://hypothes.is/groups/__world__/public?page=100
2. Go to https://hypothes.is/groups/__world__/public?page=900

### Expected behaviour
Different results should be displayed.

### Actual behaviour
The same results page is displayed. The _effective_ page number gets capped at some limit. I'm guessing this is around the (page_number / 10_000) mark.

### Notes

Browsing to the N-hundredth page (with 200 annotations per page) is not something that Elasticsearch efficiently supports. We might simply want to change the UI so that it doesn't show links to high page numbers at the bottom, which makes the issue more noticeable.