Rethink the .htaccess file

I've commented before that I'm a bit concerned about .htaccess bloat based on performance considerations and the fact that [Apache's own documentation advises against using it](https://httpd.apache.org/docs/current/howto/htaccess.html#when) if possible. From that perspective, RewriteMaps are much preferable AFAIK.

I'm not sure how relevant these considerations are in our case, but I'm also not sure how to test/measure e.g. the long-term performance impact of this.

_Originally posted by @mbollmann in https://github.com/acl-org/acl-anthology/issues/9913#issuecomment-5608015886_

The issue only mentions `.htaccess` and suggests trying `RewriteMap`s, so start by locating the active `.htaccess` file and nearby Apache/deployment config usage. Map current rewrite/redirect rules to understand what behavior is controlled there before proposing any change. No tests are named, so define done as a concrete migration plan with explicit acceptance checks (same routing behavior and documented performance rationale) after the refactor.

Written by the indexing model from the issue text.