feat: add Cron Editor tool

Visual cron expression editor with field-by-field builder, presets
select, human-readable description, and live schedule preview showing
next occurrences. Registered in tools registry with CronIcon.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/tools.tsx

@@ -1,4 +1,4 @@
-import { ColorIcon, UnitsIcon, ASCIIIcon, MediaIcon, FaviconIcon, QRCodeIcon, AnimateIcon, CalculateIcon, RandomIcon } from '@/components/AppIcons';
+import { ColorIcon, UnitsIcon, ASCIIIcon, MediaIcon, FaviconIcon, QRCodeIcon, AnimateIcon, CalculateIcon, RandomIcon, CronIcon } from '@/components/AppIcons';
 
 export interface Tool {
   /** Short display name (e.g. "Color") */
@@ -108,6 +108,17 @@ export const tools: Tool[] = [
     icon: RandomIcon,
     badges: ['Web Crypto', 'Passwords', 'UUID', 'Hashes'],
   },
+  {
+    shortTitle: 'Cron',
+    title: 'Cron Editor',
+    navTitle: 'Cron Editor',
+    href: '/cron',
+    description: 'Visual editor for cron expressions with live preview.',
+    summary:
+      'Build and validate cron expressions with an intuitive visual field editor. Get a human-readable description and preview the next upcoming scheduled runs.',
+    icon: CronIcon,
+    badges: ['Cron', 'Scheduler', 'Visual'],
+  },
   {
     shortTitle: 'Calculate',
     title: 'Calculator',