There are two old app detail URLs (#11):
* [host]/app/[package id] (https://f-droid.org/app/org.fdroid.fdroid)
* [host]/repository/browse/?fdid=[package id] (https://f-droid.org/repository/browse/?fdid=org.fdroid.fdroid)

Only the first one can be redirected using HTML.

Related to #22.