Remove focus outline/border on nav-link, add focus-visible override

- Remove .nav-link:focus from accessibility outline rules
- Add outline: none and box-shadow: none on nav-tabs .nav-link states
- Override :focus-visible with border: none, outline: none, box-shadow: none

themes/default/assets/scss/theme.scss

@@ -239,8 +239,7 @@ $header-bg-opacity: 1;
 // Enhanced accessibility styles
 .focus-visible:focus,
 .btn:focus,
-.form-control:focus,
-.nav-link:focus {
+.form-control:focus {
     outline: 3px solid #0056b3 !important;
     outline-offset: 2px !important;
     box-shadow: 0 0 0 1px #ffffff, 0 0 0 4px #0056b3 !important;
@@ -312,17 +311,25 @@ $header-bg-opacity: 1;
         border-bottom-left-radius: 0 !important;
         border-bottom-right-radius: 0 !important;
         color: var(--nav-font) !important;
+        outline: none !important;
+        box-shadow: none !important;
 
-        &:hover, &:focus {
+        &:hover, &:focus, &:focus-visible {
             isolation: auto;
             background-color: rgba(255, 255, 255, 0.1) !important;
+            border: none !important;
             border-color: transparent !important;
+            outline: none !important;
+            box-shadow: none !important;
         }
 
         &.active {
             background-color: rgba(255, 255, 255, 0.2) !important;
+            border: none !important;
             border-color: transparent !important;
             border-bottom: 2px solid var(--nav-font) !important;
+            outline: none !important;
+            box-shadow: none !important;
         }
     }