Fix: resolve 404 page asset loading on nested routes

[Bhumikagarggg]

Notes for Reviewers

• This PR fixes the 404 page asset resolution issue for nested missing routes in production (e.g., /foo/bar) by ensuring assets resolve correctly from the appropriate base path.
• The fix preserves relative asset behavior for GitHub Pages PR previews under /pr-preview/pr-<number>/.
• Important: URLs such as /pr-preview/pr-1073/j are currently served by the root GitHub Pages 404.html, not the preview folder’s 404.html. As a result, the exact preview behavior will fully work after the root 404.html is deployed with this redirect logic (post-merge production deploy).
• Tested on nested missing routes and PR preview paths to ensure styling loads correctly.

Screenshot

Signed commits

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[gemini-code-assist]

Code Review

This pull request updates the 404 error page template to support PR previews by dynamically setting the base URL and adding a redirection script. The review feedback highlights a potential issue where a missing trailing slash in the HUGO_PREVIEW_BASE_URL environment variable could cause relative asset URLs to resolve incorrectly, and provides a suggestion to safely append it.

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[github-actions]

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