Keep server.rb focused on configuration, session setup, and shared
helpers. Extract route definitions into registered Sinatra extension
modules. Exclude the registered methods from AbcSize/MethodLength
metrics — large registered methods are the idiomatic Sinatra pattern.
The admin.session_ttl value was defined in defaults, template, and
documentation but never read — sessions had no expiration. Pass it as
expire_after to Rack::Session::Cookie. A value <= 0 means persistent
(until browser close), matching the documented behaviour.
petrbalvin