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

views/bingo/sitemap.erb

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">
+<% Bingo::LOCALES.each do |l| %>
+  <url>
+    <loc><%= base_url %>/<%= l %></loc>
+<% if @lastmod %>    <lastmod><%= @lastmod.utc.strftime('%Y-%m-%d') %></lastmod>
+<% end %>    <changefreq>daily</changefreq>
+<% Bingo::LOCALES.each do |alt| %>    <xhtml:link rel="alternate" hreflang="<%= alt %>" href="<%= base_url %>/<%= alt %>"/>
+<% end %>    <xhtml:link rel="alternate" hreflang="x-default" href="<%= base_url %>/"/>
+  </url>
+<% end %>
+</urlset>