feat: Enhance ASNsNewManager with input validation, import/export functionality, and improved UI feedback for better user experience

frontend/src/BillingManager.jsx

@@ -533,7 +533,7 @@ function BillingManager() {
         </div>
         <div className="card-body">
           <div className="table-responsive">
-            <table className="table table-vcenter">
+            <table className="table card-table table-vcenter table-nowrap mb-0">
               <thead>
                 <tr>
                   <th 
@@ -603,7 +603,11 @@ function BillingManager() {
                 </tr>
               </thead>
               <tbody>
-                {paginatedData.map(item => (
+                {paginatedData.length === 0 ? (
+                  <tr>
+                    <td colSpan="8" className="text-center text-muted py-4">Ничего не найдено. Измените фильтры или параметры поиска.</td>
+                  </tr>
+                ) : paginatedData.map(item => (
                   <tr key={item.id}>
                     <td>
                       <div className="d-flex align-items-center">
@@ -712,8 +716,8 @@ function BillingManager() {
                         </button>
                       </div>
                     </td>
-                  </tr>
-                ))}
+                   </tr>
+                 ))}
               </tbody>
             </table>
           </div>