refactor: move campaign editing from modal to separate page

- Create AdminCampaignEdit page for editing campaigns
- Remove CampaignModal from AdminCampaigns
- Use centralized icons (CampaignIcon, ChartIcon added)
- Add route /admin/campaigns/:id/edit
- Add localization keys for loadError and updateError

src/App.tsx

@@ -50,6 +50,7 @@ const AdminPromoGroupCreate = lazy(() => import('./pages/AdminPromoGroupCreate')
 const AdminCampaigns = lazy(() => import('./pages/AdminCampaigns'));
 const AdminCampaignCreate = lazy(() => import('./pages/AdminCampaignCreate'));
 const AdminCampaignStats = lazy(() => import('./pages/AdminCampaignStats'));
+const AdminCampaignEdit = lazy(() => import('./pages/AdminCampaignEdit'));
 const AdminUsers = lazy(() => import('./pages/AdminUsers'));
 const AdminPayments = lazy(() => import('./pages/AdminPayments'));
 const AdminPaymentMethods = lazy(() => import('./pages/AdminPaymentMethods'));
@@ -489,6 +490,16 @@ function App() {
             </AdminRoute>
           }
         />
+        <Route
+          path="/admin/campaigns/:id/edit"
+          element={
+            <AdminRoute>
+              <LazyPage>
+                <AdminCampaignEdit />
+              </LazyPage>
+            </AdminRoute>
+          }
+        />
         <Route
           path="/admin/users"
           element={