feat(workflows): add sub-workflow inspector, breadcrumb navigation, and reference UI

Phase 3 frontend: sub-workflow node inspector with reference/inline mode toggle,
breadcrumb drill-down navigation for nested workflows, read-only view for
referenced workflows, inline workflow editing with stack propagation,
sub-workflow label badges on canvas nodes, and referential integrity error
display on delete.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/components/workflow/WorkflowGraphInspector.tsx

@@ -18,10 +18,12 @@ import type {
 } from '@shared/domain/workflow';
 import { ModelSelect, ReasoningEffortSelect } from '@renderer/components/AgentConfigFields';
 import { ConditionEditor } from '@renderer/components/workflow/ConditionEditor';
+import { SubWorkflowInspector } from '@renderer/components/workflow/SubWorkflowInspector';
 
 interface WorkflowGraphInspectorProps {
   availableModels: ReadonlyArray<ModelDefinition>;
   workflow: WorkflowDefinition;
+  workflows: ReadonlyArray<WorkflowDefinition>;
   selectedNodeId: string | null;
   selectedEdgeId: string | null;
   validationIssues?: WorkflowValidationIssue[];
@@ -30,6 +32,7 @@ interface WorkflowGraphInspectorProps {
   onNodeRemove: (nodeId: string) => void;
   onEdgeChange: (edgeId: string, patch: Partial<WorkflowEdge>) => void;
   onEdgeRemove: (edgeId: string) => void;
+  onDrillIntoSubWorkflow: (node: WorkflowNode) => void;
 }
 
 function InputField({
@@ -375,6 +378,7 @@ function EdgeInspector({
 export function WorkflowGraphInspector({
   availableModels,
   workflow,
+  workflows,
   selectedNodeId,
   selectedEdgeId,
   validationIssues,
@@ -383,6 +387,7 @@ export function WorkflowGraphInspector({
   onNodeRemove,
   onEdgeChange,
   onEdgeRemove,
+  onDrillIntoSubWorkflow,
 }: WorkflowGraphInspectorProps) {
   const selectedNode = selectedNodeId
     ? workflow.graph.nodes.find((n) => n.id === selectedNodeId)
@@ -436,6 +441,22 @@ export function WorkflowGraphInspector({
     );
   }
 
+  if (selectedNode.kind === 'sub-workflow') {
+    return (
+      <div className="p-4">
+        <SubWorkflowInspector
+          currentWorkflowId={workflow.id}
+          node={selectedNode}
+          onDrillIntoSubWorkflow={onDrillIntoSubWorkflow}
+          onNodeChange={onNodeChange}
+          onNodeConfigChange={onNodeConfigChange}
+          onNodeRemove={onNodeRemove}
+          workflows={workflows}
+        />
+      </div>
+    );
+  }
+
   return (
     <div className="p-4">
       <PlaceholderNodeInspector