Update typography scale + swap out some header styles

As far as I can tell, when we did the Clockface 3 updates we never applied the new typography scale.

This is the type scale that was created with Clockface 3:

These are the font size values that are calculated using the scale above. This matches what we have been using in Figma since Clockface 3.0 was established.

At the same time we apply these sizing updates, **we need to replace all Step 5 instances in the app with Step 4, and replace all Step 6 instances in the app with Step 5**. This is because the new steps are a great deal larger than the old (current) version.

Start by reviewing the Clockface 3 typography scale and the current typography and header styles throughout the app. Apply the scale, replace every Step 5 instance with Step 4 and every Step 6 instance with Step 5, and verify that all affected styles match the supplied scale.

Written by the indexing model from the issue text.