- Add surf.Router.AdminPrefix (additive): the admin mount path and true
when BuildRouter mounted the cabana admin, false otherwise
- serve binds with net.Listen before printing, so a busy port fails
without a misleading URL, then prints the listen address with a
browser URL and an admin status line: the admin URL, a warning naming
summer admin:create when backend_users is empty or missing, or
admin: off with the steps to add an admin controller
- The administrator count is bounded by a 2 s timeout and never fails boot
- route:list ends with the same admin status line
- surf and cabana READMEs and the console and routing docs describe the output
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