Fix theme consistency, i18n completeness, CSS variable naming, and hardcoded strings

src/app/admin/favicon/favicon-form.tsx

@@ -73,7 +73,7 @@ export function FaviconForm({ currentUrl }: { currentUrl: string | null }) {
               <img
                 src={preview}
                 alt="Favicon preview"
-                className="w-16 h-16 rounded-lg border-2 border-[var(--border)] object-contain bg-white"
+                className="w-16 h-16 rounded-lg border-2 border-[var(--border-subtle)] object-contain bg-white"
               />
               <div className="text-xs text-[var(--color-text-muted)] break-all">{preview}</div>
             </div>