Wire branding into the app shell (todo §2); render config logo + default theme, fall back to the brand mark

views/index.ejs

@@ -18,6 +18,7 @@
   brand: model.shell.brand,
   breadcrumbs: model.shell.breadcrumbs,
   nav,
+  theme: model.shell.theme,
   title: model.shell.title,
   user: model.shell.user,
 }) %>