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/src/components/AppNavigation.vue

@@ -295,7 +295,7 @@ nav,
 nav > ul {
   display: flex;
   justify-content: space-between;
-  background-color: #f9a22c;
+  background-color: #FF6B35;
   color: #000;
   padding: 0;
   margin: 0;
@@ -317,7 +317,7 @@ nav > ul > li {
 }
 
 nav > ul > li:hover {
-  background-color: #d37c06;
+  background-color: #FF8C5A;
   white-space: nowrap;
 }
 
@@ -345,7 +345,7 @@ a {
 
 .menuitem {
   cursor: pointer;
-  color: #7e471b;
+  color: #5D4037;
 }
 
 .mailbox {
@@ -363,8 +363,8 @@ a {
 
 .submenu1 {
   position: absolute;
-  border: 1px solid #7e471b;
-  background-color: #f9a22c;
+  border: 1px solid #5D4037;
+  background-color: #FF6B35;
   left: 0;
   top: 2.5em;
   max-height: 0;
@@ -388,13 +388,13 @@ a {
 .submenu1 > li {
   padding: 0.5em;
   line-height: 1em;
-  color: #7e471b;
+  color: #5D4037;
   position: relative;
 }
 
 .submenu1 > li:hover {
   color: #000;
-  background-color: #d37c06;
+  background-color: #FF8C5A;
 }
 
 .menu-icon,
@@ -419,10 +419,10 @@ a {
 
 .submenu2 {
   position: absolute;
-  background-color: #f9a22c;
+  background-color: #FF6B35;
   left: 100%;
   top: 0;
-  border: 1px solid #7e471b;
+  border: 1px solid #5D4037;
   max-height: 0;
   overflow: hidden;
   opacity: 0;
@@ -444,12 +444,12 @@ a {
 .submenu2 > li {
   padding: 0.5em;
   line-height: 1em;
-  color: #7e471b;
+  color: #5D4037;
 }
 
 .submenu2 > li:hover {
   color: #000;
-  background-color: #d37c06;
+  background-color: #FF8C5A;
 }
 
 .subsubmenu {