feat(graph): pass labels through WorkflowGraph to enable agent assignment display

## Context
This is the foundation commit for the 'Assign Archetypes to Tasks' feature.
We needed a way to display which agents are assigned to tasks directly on
the graph nodes.

## Decision Process
- User wanted to see agent assignments on DAG nodes
- We discovered that labels (including 'agent:archetype-id' format) weren't
  being passed through the WorkflowGraph component
- Added 'labels' and 'archetypes' to GraphNodeData interface

## What Changed
- WorkflowGraph now passes issue.labels to each node's data
- GraphNodeData interface updated to include labels: string[]
- Added archetypes prop for dropdown population

## Test Coverage
- Added graph-node-labels.test.tsx with 4 passing tests

## Beads: beadboard-yo5 (closed)

tests/components/graph/graph-node-labels.test.tsx

@@ -0,0 +1,32 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import fs from 'fs/promises';
+import path from 'path';
+
+// Test that GraphNodeData interface includes labels field
+test('GraphNodeData interface includes labels field', async () => {
+  const fileContent = await fs.readFile(path.join(process.cwd(), 'src/components/graph/graph-node-card.tsx'), 'utf-8');
+  // Check for labels in the interface
+  assert.ok(fileContent.includes('labels') && fileContent.includes('GraphNodeData'), 'GraphNodeData interface should include labels field');
+});
+
+// Test that GraphNodeData labels is typed as string[]
+test('GraphNodeData labels is typed as string array', async () => {
+  const fileContent = await fs.readFile(path.join(process.cwd(), 'src/components/graph/graph-node-card.tsx'), 'utf-8');
+  // Check for labels: string[] in the interface
+  assert.ok(/labels:\s*string\[\]/.test(fileContent), 'GraphNodeData labels should be typed as string[]');
+});
+
+// Test that WorkflowGraph passes issue.labels to node data
+test('WorkflowGraph passes issue.labels to node data', async () => {
+  const fileContent = await fs.readFile(path.join(process.cwd(), 'src/components/shared/workflow-graph.tsx'), 'utf-8');
+  // Check that issue.labels is passed to node data
+  assert.ok(fileContent.includes('labels: issue.labels'), 'WorkflowGraph should pass issue.labels to node data');
+});
+
+// Test that WorkflowGraph uses labels from the issue object
+test('WorkflowGraph uses labels from issue in node mapping', async () => {
+  const fileContent = await fs.readFile(path.join(process.cwd(), 'src/components/shared/workflow-graph.tsx'), 'utf-8');
+  // Check that labels is included in the data object for nodes
+  assert.ok(/data:\s*\{[^}]*labels/.test(fileContent), 'WorkflowGraph should include labels in node data object');
+});