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/components/linker/LinkResults.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { Link2, CheckCircle, XCircle } from 'lucide-react';
+import { PlugInIcon, CheckCircleIcon, XCircleIcon } from '../../icons';
 
 interface Link {
   anchor_text: string;
@@ -25,7 +25,7 @@ export const LinkResults: React.FC<LinkResultsProps> = ({
       <div className="flex items-center justify-between mb-4">
         <h3 className="text-lg font-semibold text-gray-900 dark:text-white">Linking Results</h3>
         <div className="flex items-center gap-2">
-          <Link2 className="w-5 h-5 text-blue-500" />
+          <PlugInIcon className="w-5 h-5 text-blue-500" />
           <span className="text-sm text-gray-600 dark:text-gray-400">Version {linkerVersion}</span>
         </div>
       </div>
@@ -33,7 +33,7 @@ export const LinkResults: React.FC<LinkResultsProps> = ({
       {linksAdded > 0 ? (
         <div className="space-y-4">
           <div className="flex items-center gap-2 text-green-600 dark:text-green-400">
-            <CheckCircle className="w-5 h-5" />
+            <CheckCircleIcon className="w-5 h-5" />
             <span className="font-medium">{linksAdded} link{linksAdded !== 1 ? 's' : ''} added</span>
           </div>
 
@@ -54,7 +54,7 @@ export const LinkResults: React.FC<LinkResultsProps> = ({
         </div>
       ) : (
         <div className="flex items-center gap-2 text-gray-500 dark:text-gray-400">
-          <XCircle className="w-5 h-5" />
+          <XCircleIcon className="w-5 h-5" />
           <span>No links were added to this content.</span>
         </div>
       )}