refactor: migrate from react-hot-toast to react-toastify and replace all emoji icons with Lucide React

- Replaced react-hot-toast with react-toastify (ToastContainer in providers.tsx)
- Removed @heroicons/react dependency
- Added lucide-react for consistent SVG icon system
- Migrated all 18 frontend pages from emoji icons to Lucide components
- Updated sidebar navigation, login/register, dashboard, apps, deploy,
  tickets, admin users/clusters/pools pages
- All emoji indicators (status, runtime, actions) now use proper SVG icons
- Build passes with zero TypeScript errors

frontend/src/app/register/page.tsx

@@ -4,7 +4,8 @@ import { useState } from 'react';
 import { useRouter } from 'next/navigation';
 import Link from 'next/link';
 import { useAuthStore } from '@/lib/store';
-import toast from 'react-hot-toast';
+import { toast } from 'react-toastify';
+import { Cloud } from 'lucide-react';
 
 export default function RegisterPage() {
   const [form, setForm] = useState({ email: '', password: '', firstName: '', lastName: '' });
@@ -31,7 +32,7 @@ export default function RegisterPage() {
       <div className="max-w-md w-full space-y-8 animate-slide-up">
         <div className="text-center">
           <div className="inline-flex items-center justify-center w-16 h-16 rounded-2xl bg-primary-100 mb-4">
-            <span className="text-3xl">☁️</span>
+            <Cloud className="w-8 h-8 text-primary-600" />
           </div>
           <h1 className="text-3xl font-bold text-gray-900 tracking-tight">Create your account</h1>
           <p className="mt-2 text-gray-500">