admin: per-area permissions on every route

Give each user independent read, write and delete flags per area
(invoices, bingo, users), so someone can e.g. review and remove bingo
incidents without being able to add any. The request method and path
decide the flag needed: GET is read except the new/duplicate forms, POST
to .../delete is delete, any other POST is write. Unmapped admin paths
are superuser-only, and a test enumerates every registered admin route
so a new one cannot ship without a rule.

Pages follow the same flags: nav and dashboard tiles show readable areas
only, write forms and delete buttons are hidden, and the datacenter form
is shown read-only.

Assisted-by: Claude:opus-5

lib/admin_auth.rb

@@ -1,5 +1,6 @@
 require 'rack/utils'
 require_relative 'rate_limit'
+require_relative 'admin_acl'
 
 # Session login for /admin/*, replacing the old shared HTTP Basic gate.
 #
@@ -29,6 +30,11 @@ module AdminAuth
       @current_user = user if user&.active && user.session_version == session[:uv]
     end
 
+    # For views: show a form/button only if the user may use it.
+    def can?(area, perm)
+      current_user&.can?(area, perm) || false
+    end
+
     def admin_path?(path = request.path_info)
       path == '/admin' || path.start_with?('/admin/')
     end
@@ -67,7 +73,9 @@ module AdminAuth
       if current_user.must_change_password && !request.path_info.match?(%r{\A/admin/(account/password|logout)\z})
         redirect '/admin/account/password'
       end
-      halt 403, 'Forbidden' unless current_user.superuser || request.path_info.match?(OPEN)
+      unless AdminACL.allowed?(current_user, request.request_method, request.path_info)
+        halt 403, 'You do not have access to this.'
+      end
     end
 
     app.get '/admin/login' do