fix: improve campaign stats, shared chart components, and i18n coverage

- Extract shared chart constants to constants/charts.ts
- Add TREND_STYLES to stats/constants.ts for reuse
- Fix useChartColors with MutationObserver for theme changes
- Fix DailyChart date parsing to prevent timezone shift
- Add truncate to StatCard value for overflow safety
- Fix CampaignCard copy feedback inside try block
- Add NaN validation and staleTime to AdminCampaignStats
- Replace hardcoded strings with i18n keys in Referral page
- Add missing i18n keys across all 4 locales (en, ru, zh, fa)
- Add sales stats route to AdminPanel and App router

src/App.tsx

@@ -87,6 +87,7 @@ const AdminRemnawave = lazy(() => import('./pages/AdminRemnawave'));
 const AdminRemnawaveSquadDetail = lazy(() => import('./pages/AdminRemnawaveSquadDetail'));
 const AdminEmailTemplates = lazy(() => import('./pages/AdminEmailTemplates'));
 const AdminTrafficUsage = lazy(() => import('./pages/AdminTrafficUsage'));
+const AdminSalesStats = lazy(() => import('./pages/AdminSalesStats'));
 const AdminUpdates = lazy(() => import('./pages/AdminUpdates'));
 const AdminUserDetail = lazy(() => import('./pages/AdminUserDetail'));
 const AdminBroadcastDetail = lazy(() => import('./pages/AdminBroadcastDetail'));
@@ -744,6 +745,16 @@ function App() {
             </PermissionRoute>
           }
         />
+        <Route
+          path="/admin/sales-stats"
+          element={
+            <PermissionRoute permission="stats:read">
+              <LazyPage>
+                <AdminSalesStats />
+              </LazyPage>
+            </PermissionRoute>
+          }
+        />
         <Route
           path="/admin/payment-methods"
           element={