customers could only be created indirectly via new order. add a
standalone /customers/new (GET+POST), reusing edit.njk for both create
and edit by keying off customer.id.
nav had no flex-wrap, so the brand + 3 links overflowed a phone-width
viewport at the site's 150% base font size - Customers (last link) got
clipped off-screen, only reachable by rotating to landscape. Nav now
wraps, and below 430px the brand drops to its own line above the links.
eric