bingo: SEO pass and resized photos

The bingo host fell through to asxp.io's public/, so crawlers got
asxp.io's robots.txt pointing at asxp.io's sitemap (and the keys and
invoice JS were served too). Turn static files off for BingoWeb and give
it its own robots.txt and a sitemap with hreflang alternates.

The card loaded 15.6 MB of full-size photos as cell backgrounds. Derive
480/1200 px WebP variants with ImageMagick on store (memory/area limits,
input coder pinned to the sniffed type), render cells as <img> with lazy
loading past the first two rows, and add an admin action that rebuilds
variants from the stored originals.

Head gets per-locale titles and descriptions carrying the live score,
og:image from the latest hit, Twitter card, og:locale alternates,
JSON-LD WebSite + ItemList, and Vary: Accept-Language on the redirect.

Assisted-by: Claude:opus-5

db/migrations/005_bingo_photo_variants.rb

@@ -0,0 +1,6 @@
+Sequel.migration do
+  change do
+    # true once bingo/<slug>-<hex>-{480,1200}.webp exist next to the original
+    add_column :bingo_datacenters, :photo_variants, TrueClass, null: false, default: false
+  end
+end