fix: color compound nodes by execution status in overlay

CompoundNode now uses execution overlay status to color its header:
failed (red) > completed (green) > default. Previously only used
static type-based color regardless of execution state.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/ProcessDiagram/CompoundNode.tsx

@@ -66,10 +66,17 @@ export function CompoundNode({
     onNodeClick, onNodeDoubleClick, onNodeEnter, onNodeLeave,
   };
 
-  // Gate state: filter rejected or idempotent duplicate → amber container
+  // Execution overlay state for this compound
   const ownState = node.id ? executionOverlay?.get(node.id) : undefined;
   const isGated = ownState?.filterMatched === false || ownState?.duplicateMessage === true;
-  const effectiveColor = isGated ? 'var(--amber)' : color;
+  const isCompleted = ownState?.status === 'COMPLETED';
+  const isFailed = ownState?.status === 'FAILED';
+
+  // Color priority: gated (amber) > failed (red) > completed (green) > default
+  const effectiveColor = isGated ? 'var(--amber)'
+    : isFailed ? '#C0392B'
+    : isCompleted ? '#3D7C47'
+    : color;
 
   // Dim compound when overlay is active but neither the compound nor any
   // descendant was executed in the current iteration.