feat: email templates page + client segments page with advanced filters

- Templates page: create/edit/delete/duplicate templates, category filters, placeholder insertion buttons, usage tracking
- Segments page: create/edit/delete segments with multi-criteria filter builder, preview matching clients, color picker, pin favorites
- Filter panel: multi-select dropdowns for stage/industry/tags/city/state, date range pickers, contact info toggles, search
- Added Templates + Segments to sidebar nav
- Both pages support dark mode

src/App.tsx

@@ -14,6 +14,8 @@ const SettingsPage = lazy(() => import('@/pages/SettingsPage'));
 const AdminPage = lazy(() => import('@/pages/AdminPage'));
 const NetworkPage = lazy(() => import('@/pages/NetworkPage'));
 const ReportsPage = lazy(() => import('@/pages/ReportsPage'));
+const TemplatesPage = lazy(() => import('@/pages/TemplatesPage'));
+const SegmentsPage = lazy(() => import('@/pages/SegmentsPage'));
 const InvitePage = lazy(() => import('@/pages/InvitePage'));
 const ForgotPasswordPage = lazy(() => import('@/pages/ForgotPasswordPage'));
 const ResetPasswordPage = lazy(() => import('@/pages/ResetPasswordPage'));
@@ -54,6 +56,8 @@ export default function App() {
             <Route path="emails" element={<EmailsPage />} />
             <Route path="network" element={<NetworkPage />} />
             <Route path="reports" element={<ReportsPage />} />
+            <Route path="templates" element={<TemplatesPage />} />
+            <Route path="segments" element={<SegmentsPage />} />
             <Route path="settings" element={<SettingsPage />} />
             <Route path="admin" element={<AdminPage />} />
           </Route>