feat: replace native confirm() dialogs with custom modal component

- Add ModalProvider context and useConfirm hook (confirm-modal.tsx)
- Support danger/warning/info variants with icons and colors
- Animated backdrop and dialog with CSS keyframes
- Accessible: aria-modal, role=dialog, ESC to close, auto-focus
- Replace all 6 native confirm() calls across dashboard pages
- Integrate ModalProvider in app providers

frontend/src/app/dashboard/apps/[id]/page.tsx

@@ -7,6 +7,7 @@ import { toast } from 'react-toastify';
 import type { Application, Deployment, ResourceUsage, ClusterPublic, ClusterPoolPublic } from '@/types';
 import { useState, useRef, useCallback, useEffect } from 'react';
 import { Hexagon, Rocket, Play, Square, RotateCw, Globe, Package, Server, Scale, CheckCircle, Clock, XCircle, AlertCircle, Link, GitBranch, KeyRound, FolderUp, BarChart3, ChevronDown, FileText, Monitor, Hammer, Settings, RefreshCw, Upload, Circle, Pin, Database, Eye, EyeOff, Copy, Check } from 'lucide-react';
+import { useConfirm } from '@/components/confirm-modal';
 
 const statusColors: Record<string, string> = {
   running: 'badge-green',
@@ -46,6 +47,7 @@ export default function AppDetailPage() {
   const params = useParams();
   const router = useRouter();
   const queryClient = useQueryClient();
+  const confirm = useConfirm();
   const appId = params.id as string;
   const [showLogs, setShowLogs] = useState(false);
   const [logTab, setLogTab] = useState<'pod' | 'build'>('pod');
@@ -378,10 +380,14 @@ export default function AppDetailPage() {
   const isRunning = latestStatus === 'running';
   const isInProgress = latestStatus === 'building' || latestStatus === 'deploying' || latestStatus === 'pending';
 
-  const handleDelete = () => {
-    if (confirm(`Are you sure you want to delete "${app.name}"?\n\nThis will permanently remove:\n• All Kubernetes resources (pods, services, ingress)\n• Database and volumes\n• All deployment records\n• Uploaded source code`)) {
-      deleteMutation.mutate();
-    }
+  const handleDelete = async () => {
+    const ok = await confirm({
+      title: `Delete "${app.name}"?`,
+      message: 'This will permanently remove:\n• All Kubernetes resources (pods, services, ingress)\n• Database and volumes\n• All deployment records\n• Uploaded source code',
+      confirmText: 'Delete',
+      variant: 'danger',
+    });
+    if (ok) deleteMutation.mutate();
   };
 
   return (