Topbar active links, algorithm icons & styles

Add active state support to topbar links (routerLinkActive) and CSS underline/hover styling; expose icons for algorithm categories and render them in the algorithms list. Update AlgorithmCategory interface and AlgorithmsService to include icon names, import MatIconModule where needed, and adjust algorithms template to show icon, title and description layout. Global style tweaks: dark theme background, canvas shadows, card hover/gradient accents, and new styles for algorithm cards and page title for improved visual polish.

src/app/layout/topbar/topbar.component.scss

@@ -52,6 +52,37 @@
     justify-content: center;
 }
 
+.nav a {
+    opacity: 0.72;
+    transition: opacity 150ms ease;
+    position: relative;
+
+    &::after {
+        content: '';
+        position: absolute;
+        bottom: 4px;
+        left: 10px;
+        right: 10px;
+        height: 2px;
+        background: currentColor;
+        border-radius: 2px;
+        transform: scaleX(0);
+        transition: transform 200ms ease;
+    }
+
+    &:hover {
+        opacity: 1;
+    }
+
+    &.active {
+        opacity: 1;
+
+        &::after {
+            transform: scaleX(1);
+        }
+    }
+}
+
 .nav-menu-btn {
     display: none;
 }