fix: refine AI providers and auth files styling and layout alignment

- Remove inset box-shadow from stat badges for cleaner appearance
  - Add modelCountLabel style for consistent model count display
  - Refactor model count layout in AiProvidersPage
  - Add openaiTestButton style for proper button height alignment
  - Add item-actions flexbox utility style to layout.scss

src/styles/layout.scss

@@ -404,6 +404,11 @@
       font-weight: 700;
       color: var(--text-primary);
     }
+
+    .item-actions {
+      display: flex;
+      gap: $spacing-sm;
+    }
   }
 
   .toggle-advanced {