Give it a container and a page of its own

A Dockerfile that builds the bundle and serves it from nginx, matching the
three games already on the site, and the metadata a page needs when it is
somewhere rather than on a laptop: canonical, Open Graph, the two JSON-LD
blocks, and a noscript that describes the game rather than showing an empty
div to anybody who does not run scripts.

No dev proxy, unlike its siblings. They post scores to a shared service and
this one has nothing to post: a game of Diplomacy is not a number, and a
leaderboard reading "reached eleven centres" would be a worse thing to know
about somebody than nothing at all.

The favicon is seven powers round a board in the seven colours the map uses,
with the one supply centre in the middle they are all looking at -- drawn
here rather than drafted in a tool, like every other mark in this
repository.

And a way back out, absolute rather than "/": this is served from a
subdirectory in production and from the root in development, so the relative
answer is right in one of those and points at the game itself in the other.

public/favicon.svg

@@ -0,0 +1,16 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Great Powers">
+  <!-- Seven powers round a board in the seven colours the map uses, and the
+       one supply centre in the middle that they are all looking at. Drawn
+       rather than drafted in a tool, like every other mark in this
+       repository. -->
+  <rect width="64" height="64" fill="#e6d8ba"/>
+  <g stroke="#2b2318" stroke-width="2.5">
+    <circle cx="32" cy="10.5" r="5.5" fill="#d4736c"/>
+    <circle cx="50.7" cy="21.3" r="5.5" fill="#e7a8c8"/>
+    <circle cx="50.7" cy="42.7" r="5.5" fill="#89b4dd"/>
+    <circle cx="32" cy="53.5" r="5.5" fill="#9d9d9d"/>
+    <circle cx="13.3" cy="42.7" r="5.5" fill="#93cc9e"/>
+    <circle cx="13.3" cy="21.3" r="5.5" fill="#b08fc4"/>
+    <circle cx="32" cy="32" r="6.5" fill="#e8dc8c"/>
+  </g>
+</svg>