feat: replace campaign creation modal with dedicated page

- Create AdminCampaignCreate.tsx with full form for new campaigns
- Update AdminCampaigns.tsx to navigate to create page
- Keep edit functionality as modal
- Add route /admin/campaigns/create in App.tsx

src/App.tsx

@@ -41,6 +41,7 @@ const AdminBroadcasts = lazy(() => import('./pages/AdminBroadcasts'));
 const AdminBroadcastCreate = lazy(() => import('./pages/AdminBroadcastCreate'));
 const AdminPromocodes = lazy(() => import('./pages/AdminPromocodes'));
 const AdminCampaigns = lazy(() => import('./pages/AdminCampaigns'));
+const AdminCampaignCreate = lazy(() => import('./pages/AdminCampaignCreate'));
 const AdminUsers = lazy(() => import('./pages/AdminUsers'));
 const AdminPayments = lazy(() => import('./pages/AdminPayments'));
 const AdminPaymentMethods = lazy(() => import('./pages/AdminPaymentMethods'));
@@ -358,6 +359,16 @@ function App() {
             </AdminRoute>
           }
         />
+        <Route
+          path="/admin/campaigns/create"
+          element={
+            <AdminRoute>
+              <LazyPage>
+                <AdminCampaignCreate />
+              </LazyPage>
+            </AdminRoute>
+          }
+        />
         <Route
           path="/admin/users"
           element={