Align logo image and text in site header

Summary: Ref T15666. Center wordmark vertically to align with logo in site header.

Test Plan:

• Check alignment visually.
• With browser DevTools, verify that wordmark is 44px tall.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15666

Differential Revision: https://we.phorge.it/D25467