Fix proper 404

[Charul192]

What has changed?

• Fixed the broken 404 page on the documentation website.
• Replaced the default 404 UI with an automatic redirect using window.location.replace("/docs").
• This ensures that users visiting a non-existent route are cleanly redirected to the main documentation page without extra browser history entries.

This PR Resolves #2975

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Ran npm run build and npm run serve
• Navigated to random invalid routes like /abc, /random-page, /something
• Verified instant redirect to /docs
• Confirmed there are no extra entries added in browser history
• Checked behaviour in both light and dark mode

ScreenRecording: https://github.com/user-attachments/assets/6079aaa5-6dd6-4247-97d7-5056692e484a

Checklist:

• [x] My code follows the style guidelines of this project.
• [x] I have performed a self-review of my own code.
• [x] My PR contains only the required file changes.