automc ui: per-route active connection counts + total in header

Pulls mc_router_active_connections + mc_router_server_active_connections
from the Prometheus default registry on every /api/routes call. UI
gains an Active column on the routes table and the header subtitle
shows "N routes · M active conn".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/automc/static/index.html

@@ -74,6 +74,7 @@
         <tr>
           <th>Server address (host)</th>
           <th>Backend</th>
+          <th style="text-align:right;">Active</th>
         </tr>
       </thead>
       <tbody id="route-rows"></tbody>
@@ -106,11 +107,14 @@ async function refreshRoutes() {
       count.textContent = '(' + j.routes.length + ')';
       for (const r of j.routes) {
         const tr = document.createElement('tr');
-        tr.innerHTML = '<td>' + r.server_address + '</td><td>' + r.backend + '</td>';
+        tr.innerHTML = '<td>' + r.server_address + '</td>' +
+                       '<td>' + r.backend + '</td>' +
+                       '<td style="text-align:right;font-variant-numeric:tabular-nums;">' + r.active_connections + '</td>';
         rows.appendChild(tr);
       }
     }
-    document.getElementById('meta').textContent = '— ' + j.routes.length + ' routes';
+    document.getElementById('meta').textContent =
+      '— ' + j.routes.length + ' routes · ' + (j.total_connections || 0) + ' active conn';
   } catch (e) {
     document.getElementById('meta').textContent = '— api error';
   }