Remove --bs-nav-tabs CSS variables from theme, use direct !important overrides

- Remove --bs-nav-tabs-border-radius/width/color from theme.css
- Use border: none !important and border-radius: 0 !important directly
- Override all Bootstrap --bs-dropdown-* variables completely
- Add gap: 0 on .nav-tabs

themes/default/assets/css/theme.css

@@ -221,12 +221,10 @@
   }
 }
 .nav-tabs {
-  --bs-nav-tabs-border-radius: 0;
-  --bs-nav-tabs-border-width: 0;
-  --bs-nav-tabs-border-color: transparent;
   background-color: transparent !important;
   border: none !important;
   border-radius: 0 !important;
+  gap: 0 !important;
 }
 .nav-tabs .nav-link {
   background-color: transparent !important;

themes/default/assets/css_compiled/theme.css

@@ -221,12 +221,10 @@
   }
 }
 .nav-tabs {
-  --bs-nav-tabs-border-radius: 0;
-  --bs-nav-tabs-border-width: 0;
-  --bs-nav-tabs-border-color: transparent;
   background-color: transparent !important;
   border: none !important;
   border-radius: 0 !important;
+  gap: 0 !important;
 }
 .nav-tabs .nav-link {
   background-color: transparent !important;

themes/default/assets/scss/theme.scss

@@ -288,12 +288,10 @@ $header-bg-opacity: 1;
 
 // Remove nav-tabs background so it inherits from parent
 .nav-tabs {
-    --bs-nav-tabs-border-radius: 0;
-    --bs-nav-tabs-border-width: 0;
-    --bs-nav-tabs-border-color: transparent;
     background-color: transparent !important;
     border: none !important;
     border-radius: 0 !important;
+    gap: 0 !important;
 
     .nav-link {
         background-color: transparent !important;