chore: replace Unicode/emoji icons with Lucide React

Adds lucide-react and replaces all HTML entity and emoji icons across
the UI with proper SVG icon components. Tree-shaken — only imported
icons are bundled.

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

ui/src/components/ProcessDiagram/NodeToolbar.tsx

@@ -1,4 +1,6 @@
 import { useCallback, useRef, useState } from 'react';
+import { Search, Footprints, Droplets, Ellipsis } from 'lucide-react';
+import type { LucideIcon } from 'lucide-react';
 import type { NodeAction } from './types';
 import styles from './ProcessDiagram.module.css';
 
@@ -14,11 +16,11 @@ interface NodeToolbarProps {
   onMouseLeave: () => void;
 }
 
-const ACTIONS: { icon: string; action: NodeAction; title: string }[] = [
-  { icon: '\uD83D\uDD0D', action: 'inspect', title: 'Inspect' },
-  { icon: '\uD83D\uDC63', action: 'toggle-trace', title: 'Toggle tracing' },
-  { icon: '\uD83D\uDEB0', action: 'configure-tap', title: 'Configure tap' },
-  { icon: '\u22EF', action: 'copy-id', title: 'Copy ID' },
+const ACTIONS: { Icon: LucideIcon; action: NodeAction; title: string }[] = [
+  { Icon: Search, action: 'inspect', title: 'Inspect' },
+  { Icon: Footprints, action: 'toggle-trace', title: 'Toggle tracing' },
+  { Icon: Droplets, action: 'configure-tap', title: 'Configure tap' },
+  { Icon: Ellipsis, action: 'copy-id', title: 'Copy ID' },
 ];
 
 export function NodeToolbar({
@@ -41,7 +43,7 @@ export function NodeToolbar({
             onAction(nodeId, a.action);
           }}
         >
-          {a.icon}
+          <a.Icon size={14} />
         </button>
       ))}
     </div>