Give Harbormaster build steps a "View" page

Summary:
Fixes T9519. Right now, build steps go straight from the build to the edit screen.

This means that there's no way to see their edit history or review details without edit permission. In particular, this makes it a bit harder to catch the Drydock Blueprint authorization warnings from T9519.

• Add a standard view screen.
• Add a little warning callout to blueprint authorizations.

This also does a bit of a touchup on the weird dropshadow element from T9586. Maybe not totally design-approved now but it's less ugly, at least.

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9519

Differential Revision: https://secure.phabricator.com/D14330