Localise the recurrence rule descriptions

[borgoat]

Currently, we either use the recurrence rule name (daily, weekly, etc..) in English (such as in the "create schedule" form), or with a manually localised name for the specific instances we created. Both approaches are dirty, the former because it would be the only non-translated lines in the app, the latter because it wouldn't work for custom rules that we want to support at some time.

A better approach would be to extend RruleL10n in the rrule package we use (and possibly contribute back the rules), probably asking Copilot to do its magic.