Add Page that Shows Preamble Before Start of Competition

Using the API added in https://github.com/basalt-rs/basalt-server/issues/34, show a screen before the competition starts with the preamble and information about the competition, such as the time limit.

Start by reading the API described in issue #34 and identify the existing competition-page entry point. Add a screen shown before the competition starts that displays the preamble and competition information such as the time limit. Done means the preamble and relevant information are visible before the competition begins.

Written by the indexing model from the issue text.