Split SchildiChat ecosystem entry to mirror Element classic

SchildiChat is a fork of Element web and classic. The latter are actually 3 separate projects, of which Schildi forks 2. Element has recently split its entry into web and mobile to distinguish between the still supported web app and the mobile apps which are slowly moving towards deprecation.

Schildi Web is effectively unmaintained in favor of the upcoming SchildiRevenge client (which we should also add, as an alpha client). I have agreed with @SpiritCroc to mark Web as obsolete.

Schildi Android is legacy but still supported for now.

The names of affected apps should be updated to "legacy", matching https://schildi.chat/legacy/.

Find the SchildiChat ecosystem entry and compare it with the split Element web and mobile entries. Update the affected names to identify Schildi Web as obsolete and Schildi Android as legacy, and add SchildiRevenge as an alpha client; verify the result against the legacy naming at schildi.chat/legacy/.

Written by the indexing model from the issue text.