Add sale management feature for admin panel

- Add database migration for sale fields (percentage, active, dates)
- Update API to handle sale operations and bulk updates
- Create SaleManager component for admin interface
- Update FilamentTableV2 to display sale prices on frontend
- Add sale column in admin dashboard
- Implement sale price calculations with strikethrough styling

app/upadaj/dashboard/page.tsx

@@ -5,6 +5,7 @@ import { useRouter } from 'next/navigation';
 import { filamentService, colorService } from '@/src/services/api';
 import { Filament } from '@/src/types/filament';
 import { trackEvent } from '@/src/components/MatomoAnalytics';
+import { SaleManager } from '@/src/components/SaleManager';
 // Removed unused imports for Bambu Lab color categorization
 import '@/src/styles/select.css';
 
@@ -339,6 +340,11 @@ export default function AdminDashboard() {
                       Obriši izabrane ({selectedFilaments.size})
                     </button>
                   )}
+                  <SaleManager 
+                    filaments={filaments}
+                    selectedFilaments={selectedFilaments}
+                    onSaleUpdate={fetchFilaments}
+                  />
                   <button
                     onClick={() => router.push('/')}
                     className="flex-1 sm:flex-initial px-3 sm:px-4 py-2 bg-blue-500 text-white rounded hover:bg-blue-600 text-sm sm:text-base"
@@ -474,6 +480,7 @@ export default function AdminDashboard() {
                 <th onClick={() => handleSort('cena')} className="px-6 py-3 text-left text-xs font-medium text-gray-500 dark:text-gray-300 uppercase tracking-wider cursor-pointer hover:bg-gray-100 dark:hover:bg-gray-700">
                   Cena {sortField === 'cena' && (sortOrder === 'asc' ? '↑' : '↓')}
                 </th>
+                <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 dark:text-gray-300 uppercase tracking-wider">Popust</th>
                 <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 dark:text-gray-300 uppercase tracking-wider">Akcije</th>
               </tr>
             </thead>
@@ -565,6 +572,22 @@ export default function AdminDashboard() {
                       );
                     })()}
                   </td>
+                  <td className="px-6 py-4 whitespace-nowrap text-sm">
+                    {filament.sale_active && filament.sale_percentage ? (
+                      <div>
+                        <span className="inline-flex items-center px-2.5 py-0.5 rounded-full text-xs font-medium bg-purple-100 text-purple-800 dark:bg-purple-900 dark:text-purple-200">
+                          -{filament.sale_percentage}%
+                        </span>
+                        {filament.sale_end_date && (
+                          <div className="text-xs text-gray-500 dark:text-gray-400 mt-1">
+                            do {new Date(filament.sale_end_date).toLocaleDateString('sr-RS')}
+                          </div>
+                        )}
+                      </div>
+                    ) : (
+                      <span className="text-gray-400 dark:text-gray-500">-</span>
+                    )}
+                  </td>
                   <td className="px-6 py-4 whitespace-nowrap text-sm font-medium">
                     <button
                       onClick={() => {