Add Books nav link and bookshop scaffold

Wires up bookshop_base_url and a "Books" nav entry ahead of Cate's
first title — content/books gets a coming-soon placeholder, and the
book single/ARC-redeem templates (copied from michaelferrara-site)
are ready to use once there's a real book page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

hugo.toml

@@ -13,6 +13,12 @@ disableKinds = ["taxonomy", "term"]
   description = "TODO: one-line author bio/description"
   author = "Cate Conners"
   eec_base_url = "https://eec.cateconners.com"
+  bookshop_base_url = "https://shop.cateconners.com"
+
+[[menu.main]]
+  name = "Books"
+  url = "/books/"
+  weight = 10
 
 [[menu.footer]]
   name = "Contact"