bingo: add, delete and reorder datacenters from admin

The card was fixed to the 25 seeded rows, so a new site such as
IXcellerate MOS7 (34 MW, under construction) could only be shoehorned in
by overwriting an existing row. Add create and delete (cascading to
incidents), make position an insert that shifts the rest, and keep
positions dense. More than 25 rows are allowed: the card shows the first
25 and the rest wait in reserve. "Sort by MW" re-ranks by the parsed
power figure, unknown last.

Assisted-by: Claude:opus-5

views/admin/bingo/index.erb

@@ -67,6 +67,11 @@
 
 <section class="section">
     <h2>Card</h2>
+    <p><a href="/admin/bingo/dc/new">+ Add datacenter</a> · positions 1–<%= Bingo::SIZE**2 %> are on the card, the rest are reserve</p>
+    <form method="post" action="/admin/bingo/sort" onsubmit="return confirm('Re-rank every datacenter by MW? Manual ordering is lost.')">
+        <input type="hidden" name="authenticity_token" value="<%= csrf_token %>" />
+        <button type="submit" class="link-button">⇅ Sort by MW (unknown last)</button>
+    </form>
     <form method="post" action="/admin/bingo/photos/import">
         <input type="hidden" name="authenticity_token" value="<%= csrf_token %>" />
         <button type="submit" class="link-button">↻ Import all missing photos from their source URLs</button>
@@ -80,6 +85,9 @@
         <thead><tr><th>#</th><th>Photo</th><th>Name</th><th>Operator</th><th class="num">MW</th><th>Status</th><th class="num">Incidents</th><th></th></tr></thead>
         <tbody>
             <% @dcs.each do |dc| %>
+                <% if dc.position == Bingo::SIZE**2 + 1 %>
+                    <tr><td colspan="8" class="optional">— reserve (not on the card) —</td></tr>
+                <% end %>
                 <tr>
                     <td class="mono"><%= dc.position %></td>
                     <td><% if dc.photo_file %><img src="/admin/bingo/p/<%= dc.photo_file %>" alt="" width="64" height="40" style="object-fit: cover" /><% else %>—<% end %></td>