feat: Replace flat phase sidebar with vertical execution graph

Phases are now grouped by dependency depth using groupPhasesByDependencyLevel.
Single-phase layers render as compact nodes, multi-phase layers are wrapped in
a dashed "PARALLEL" container. Connectors between layers turn green when prior
layers are all completed. Staggered entrance animation per layer.

apps/web/src/index.css

@@ -279,6 +279,11 @@
   100% { background-position: 200% 0; }
 }
 
+@keyframes graph-layer-enter {
+  from { opacity: 0; transform: translateY(4px); }
+  to { opacity: 1; transform: translateY(0); }
+}
+
 /* Global focus-visible styles */
 *:focus-visible {
   outline: 2px solid hsl(var(--ring));