/status: show HTTP request headers and client IP.

Show the HTTP request headers and the client IP on the /status page.
This is for debugging request headers added by reverse proxies such as
Cloudflare and Nginx, and for making sure the client IP is correctly set
by the X-Forwarded-For header.

app/views/status/show.html.erb

@@ -34,5 +34,14 @@
 
       <%= render "list", hash: @status.serializable_hash[:redis][:info] %>
     </details>
+
+    <h2>Request</h2>
+
+    <details>
+      <summary>
+        IP: <%= @status.request.remote_ip %>
+      </summary>
+      <%= render "list", hash: @status.serializable_hash[:headers] %>
+    </details>
   </div>
 </div>