Refactor frontend components to use new icon imports and improve default values

- Updated `EnhancedMetricCard` to set a default accent color to blue.
- Replaced `lucide-react` icons with custom icons in `LinkResults`, `OptimizationScores`, and various pages in the Automation and Optimizer sections.
- Enhanced button layouts in `AutomationRules`, `Tasks`, and `ContentSelector` for better alignment and user experience.
- Improved loading indicators across components for a more consistent UI experience.

frontend/src/pages/Linker/ContentList.tsx

@@ -7,7 +7,7 @@ import { fetchContent, Content as ContentType } from '../../services/api';
 import { useToast } from '../../components/ui/toast/ToastContainer';
 import { SourceBadge, ContentSource } from '../../components/content/SourceBadge';
 import { LinkResults } from '../../components/linker/LinkResults';
-import { Link2, Loader2 } from 'lucide-react';
+import { PlugInIcon } from '../../icons';
 import { useSectorStore } from '../../store/sectorStore';
 import { usePageSizeStore } from '../../store/pageSizeStore';
 
@@ -161,12 +161,12 @@ export default function LinkerContentList() {
                           >
                             {isProcessing ? (
                               <>
-                                <Loader2 className="w-4 h-4 animate-spin" />
+                                <div className="w-4 h-4 border-2 border-white border-t-transparent rounded-full animate-spin" />
                                 Processing...
                               </>
                             ) : (
                               <>
-                                <Link2 className="w-4 h-4" />
+                                <PlugInIcon className="w-4 h-4" />
                                 Add Links
                               </>
                             )}