fix: improve ghost button visibility in admin dark mode

Update ghost button variant to use proper dark mode colors:
- Add dark:hover:bg-neutral-700 for hover state
- Add dark:text-neutral-300 for better icon/text visibility
- Fixes too-dark edit and view gallery buttons in Events table

frontend/src/components/common/Button.tsx

@@ -32,7 +32,7 @@ export const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
       primary: 'btn-primary',
       secondary: 'btn-secondary',
       outline: 'btn-outline',
-      ghost: 'bg-transparent hover:bg-neutral-100 text-neutral-700',
+      ghost: 'bg-transparent hover:bg-neutral-100 dark:hover:bg-neutral-700 text-neutral-600 dark:text-neutral-300',
     };
 
     const sizes = {