feat: replace Unicode diagram icons with lucide SVG icons

Each of the ~40 node types now has a distinct, semantically meaningful
lucide icon rendered as crisp SVG paths. Compound node headers also
show their icon left-aligned in the header bar.

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

ui/src/components/ProcessDiagram/DiagramNode.tsx

@@ -1,7 +1,7 @@
 import type { DiagramNode as DiagramNodeType } from '../../api/queries/diagrams';
 import type { NodeConfig } from './types';
 import type { NodeExecutionState } from '../ExecutionDiagram/types';
-import { colorForType, iconForType } from './node-colors';
+import { colorForType, iconForType, type IconElement } from './node-colors';
 import { ConfigBadge } from './ConfigBadge';
 
 const TOP_BAR_HEIGHT = 6;
@@ -37,7 +37,7 @@ export function DiagramNode({
   const w = node.width ?? 120;
   const h = node.height ?? 40;
   const color = colorForType(node.type);
-  const icon = iconForType(node.type);
+  const iconElements = iconForType(node.type);
 
   // Extract label parts: type name and detail
   const typeName = node.type?.replace(/^EIP_/, '').replace(/_/g, ' ') ?? '';
@@ -116,10 +116,14 @@ export function DiagramNode({
         <rect x={TEXT_LEFT} y={TOP_BAR_HEIGHT} width={w - TEXT_LEFT - TEXT_RIGHT_PAD} height={h - TOP_BAR_HEIGHT} />
       </clipPath>
 
-      {/* Icon */}
-      <text x={14} y={h / 2 + 4} fill={statusColor ?? color} fontSize={14}>
-        {icon}
-      </text>
+      {/* Icon (lucide 24×24 scaled to 14px) */}
+      <g transform={`translate(6, ${h / 2 - 7}) scale(0.583)`}>
+        {iconElements.map((el: IconElement, i: number) =>
+          'd' in el
+            ? <path key={i} d={el.d} fill="none" stroke={statusColor ?? color} strokeWidth={2} strokeLinecap="round" strokeLinejoin="round" />
+            : <circle key={i} cx={el.cx} cy={el.cy} r={el.r} fill="none" stroke={statusColor ?? color} strokeWidth={2} />
+        )}
+      </g>
 
       {/* Type name + detail (clipped to available width) */}
       <g clipPath={`url(#clip-${node.id})`}>