feat: Enhance modal button behavior and validation feedback

- Updated modal button handling to disable all buttons by default, with exceptions for specific button types (e.g., cancel, close, delete).
- Introduced a new validation mechanism that visually indicates empty required fields with red borders and error messages after a delay.
- Improved the `useDialogAutoValidation` hook to manage button states based on field validation, ensuring a smoother user experience.
- Added CSS animations to prevent flickering during validation state changes.

Made-with: Cursor

frontend/components/v2/V2Select.tsx

@@ -167,7 +167,10 @@ const DropdownSelect = forwardRef<HTMLButtonElement, {
           )}
           style={style}
         >
-          <span className="truncate flex-1 text-left">
+          <span
+            className="truncate flex-1 text-left"
+            {...(selectedLabels.length === 0 ? { "data-placeholder": placeholder } : {})}
+          >
             {selectedLabels.length > 0
               ? multiple 
                 ? `${selectedLabels.length}개 선택됨`