feat: Reports & Analytics page, CSV export, notification bell in header

- Reports page with overview stats, client growth chart, email activity chart
- Engagement breakdown (engaged/warm/cooling/cold) with stacked bar
- Industry and tag distribution charts
- At-risk client lists (cold + cooling)
- CSV export button downloads all clients
- Notification bell in top bar: overdue events, upcoming events, stale clients, pending drafts
- Dismissable notifications with priority indicators
- Added Reports to sidebar nav between Network and Settings

src/App.tsx

@@ -11,6 +11,7 @@ import EmailsPage from '@/pages/EmailsPage';
 import SettingsPage from '@/pages/SettingsPage';
 import AdminPage from '@/pages/AdminPage';
 import NetworkPage from '@/pages/NetworkPage';
+import ReportsPage from '@/pages/ReportsPage';
 import InvitePage from '@/pages/InvitePage';
 import ForgotPasswordPage from '@/pages/ForgotPasswordPage';
 import ResetPasswordPage from '@/pages/ResetPasswordPage';
@@ -50,6 +51,7 @@ export default function App() {
           <Route path="events" element={<EventsPage />} />
           <Route path="emails" element={<EmailsPage />} />
           <Route path="network" element={<NetworkPage />} />
+          <Route path="reports" element={<ReportsPage />} />
           <Route path="settings" element={<SettingsPage />} />
           <Route path="admin" element={<AdminPage />} />
         </Route>