Redesigned dashboard navigation, Ko-fi support

The dashboard navigation got a cleaner, Finder-style layout: a slim icon rail for the main sections, with a workspace switcher and tabs up top instead of a deep sidebar tree. We also added Ko-fi as a payment provider, popular with the Ghost community for tips and memberships.

• New breadcrumb + tabs navigation across the whole dashboard
• Ko-fi connection: sync donations and memberships to Ghost access
• Six payment providers now supported end to end