Fix/统一修复modal样式失效 (#122)

之前遇到几次弹窗的样式不生效,bug 现在在画布agent的删除对话弹窗又出现了,
这个pr把类似的修改集中到最下层的UnifiedModal,适用于所有的modal,
一些特殊的modal有特殊处理.

画布agent的删除对话弹窗
![shotmd-1785399342.jpg](/attachments/d63d7dc6-bf7e-4f13-bfe8-bc4716cd798f)

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Co-authored-by: 段舒康 <kdletters@qq.com>
Reviewed-on: http://192.168.35.82/git/GenarrativeAI/Genarrative/pulls/122
Reviewed-by: 段舒康 <kdletters@qq.com>
Co-authored-by: 王德宇 <kvtodev@outlook.com>
Co-committed-by: 王德宇 <kvtodev@outlook.com>

src/components/common/PlatformImagePreviewModal.test.tsx

@@ -103,6 +103,7 @@ test('renders full-screen image preview with zoom controls and dark backdrop', (
   expect(
     dialog.parentElement?.className.includes('!bg-black'),
   ).toBe(true);
+  expect(dialog.parentElement?.className).not.toContain('platform-theme--');
   expect(screen.getByRole('button', { name: '放大图片' })).toBeTruthy();
   expect(screen.getByRole('button', { name: '缩小图片' })).toBeTruthy();
   expect(screen.getByRole('button', { name: '重置图片缩放' })).toBeTruthy();