feat: make stats bar cells clickable to filter by state

Clicking deployed/testing/degraded sets the state filter to that
value. Clicking total clears all filters. Hover style added.

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

css/app.css

@@ -153,6 +153,8 @@ main { flex: 1; }
 }
 
 .stat-cell:last-child { border-right: none; }
+.stat-clickable { cursor: pointer; user-select: none; }
+.stat-clickable:hover { background: var(--bg2); }
 
 .stat-label {
   font-size: 10px;