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/optimizer/OptimizationScores.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { TrendingUp, TrendingDown, Minus } from 'lucide-react';
+import { ArrowUpIcon, ArrowDownIcon } from '../../icons';
 
 interface ScoreData {
   seo_score: number;
@@ -39,9 +39,9 @@ export const OptimizationScores: React.FC<OptimizationScoresProps> = ({
   const getChangeIcon = (current: number, previous?: number) => {
     if (!previous) return null;
     const diff = current - previous;
-    if (diff > 0) return <TrendingUp className="w-4 h-4 text-green-600" />;
-    if (diff < 0) return <TrendingDown className="w-4 h-4 text-red-600" />;
-    return <Minus className="w-4 h-4 text-gray-400" />;
+    if (diff > 0) return <ArrowUpIcon className="w-4 h-4 text-green-600" />;
+    if (diff < 0) return <ArrowDownIcon className="w-4 h-4 text-red-600" />;
+    return <span className="w-4 h-4 text-gray-400">—</span>;
   };
 
   const getChangeText = (current: number, previous?: number) => {