fix: remove stacks count from stats bar

Stacks are always just production/development — counting them adds
no useful information to the dashboard summary.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

js/ui.js

@@ -39,7 +39,6 @@ async function renderDashboard() {
     <div class="stat-cell"><div class="stat-label">deployed</div><div class="stat-value">${states['deployed'] || 0}</div></div>
     <div class="stat-cell"><div class="stat-label">testing</div><div class="stat-value amber">${states['testing'] || 0}</div></div>
     <div class="stat-cell"><div class="stat-label">degraded</div><div class="stat-value red">${states['degraded'] || 0}</div></div>
-    <div class="stat-cell"><div class="stat-label">stacks</div><div class="stat-value">${(await getDistinctStacks()).length}</div></div>
   `;
 
   await populateStackFilter();