Update color palette and styles across components for improved visual consistency

- Changed theme color in index.html to a brighter orange for better aesthetics.
- Introduced a modern color palette in styles.scss for enhanced readability and consistency.
- Updated various components (AppFooter, AppNavigation, DialogWidget, etc.) to utilize new color variables, ensuring a cohesive look throughout the application.
- Adjusted button styles and hover effects for improved user interaction feedback.
- Enhanced background colors and text colors for better contrast and visibility.

frontend/index.html

@@ -21,7 +21,7 @@
     <meta name="twitter:title" content="YourPart – Community, Chat, Forum, Vokabeltrainer, Falukant & Minispiele" />
     <meta name="twitter:description" content="Community, Chat, Forum, soziales Netzwerk, Vokabeltrainer zum Sprachen lernen, das Aufbauspiel Falukant sowie Minispiele – jetzt in der Beta testen." />
 
-    <meta name="theme-color" content="#F9A22C" />
+    <meta name="theme-color" content="#FF8C5A" />
 
     <script type="application/ld+json">
     {