chore(about): 🔗 更新官方网址为 https://markdown.fit (#49)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jorben

src/renderer/components/About.tsx

@@ -50,7 +50,7 @@ const About: React.FC = () => {
           {t('about.subtitle')}
         </Text>
         <Space style={{ marginTop: 16 }}>
-          <Button onClick={() => handleOpenLink('https://github.com/MarkPDFdown/markpdfdown-desktop')}>
+          <Button onClick={() => handleOpenLink('https://markdown.fit')}>
             {t('about.buttons.website')}
           </Button>
           <Button onClick={() => handleOpenLink('https://github.com/MarkPDFdown/markpdfdown-desktop/blob/master/LICENSE')}>

src/renderer/components/__tests__/About.test.tsx

@@ -127,7 +127,7 @@ describe('About', () => {
       const websiteButton = screen.getByText('Website')
       fireEvent.click(websiteButton)
 
-      expect(mockWindowOpen).toHaveBeenCalledWith('https://github.com/MarkPDFdown/markpdfdown-desktop', '_blank')
+      expect(mockWindowOpen).toHaveBeenCalledWith('https://markdown.fit', '_blank')
     })
 
     it('should open license link when License button is clicked', () => {