feat(frontend): add Dashboard page and components for #53

Implement the main dashboard homepage with:
- WelcomeHeader: Personalized greeting with user name
- DashboardQuickStats: Stats cards for projects, agents, issues, approvals
- RecentProjects: Dynamic grid showing 3-6 recent projects
- PendingApprovals: Action-required approvals section
- EmptyState: Onboarding experience for new users
- useDashboard hook: Mock data fetching with React Query

The dashboard serves as the authenticated homepage at /(authenticated)/
and provides quick access to all project management features.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/app/[locale]/(authenticated)/page.tsx

@@ -0,0 +1,23 @@
+/**
+ * Dashboard Page
+ *
+ * Main authenticated homepage showing:
+ * - Quick stats overview
+ * - Recent projects
+ * - Pending approvals
+ * - Real-time activity feed
+ *
+ * @see Issue #53
+ */
+
+import { Metadata } from 'next';
+import { Dashboard } from '@/components/dashboard';
+
+export const metadata: Metadata = {
+  title: 'Dashboard',
+  description: 'Overview of your projects, agents, and activity',
+};
+
+export default function DashboardPage() {
+  return <Dashboard />;
+}