bingo: optional prose per datacenter page

The datacenter pages carry only generated sentences, which is thin
content to rank on. Migration 015 adds about_ru/en/uk, edited in the
admin form and rendered as paragraphs below the facts.

There is deliberately no fallback to ru: Russian prose on the English
page would hurt more than an absent paragraph.

Assisted-by: Claude:opus-5

lib/bingo_admin.rb

@@ -4,7 +4,7 @@ require 'uri'
 # Registered into AsxpioWeb, so AdminAuth (HTTP Basic) and CSRF apply.
 module BingoAdmin
   DC_TEXT = %w[name_ru name_en name_uk city_ru city_en city_uk operator mw mw_type status
-               photo_credit photo_source_url info_url].freeze
+               photo_credit photo_source_url info_url about_ru about_en about_uk].freeze
 
   module Helpers
     def bingo_public_url