fix: file link in overlay with custom backend

[sapphi-red]

Description

Vite server listens on the same host with the client script. import uses import.meta.url as the base, but fetch uses location.href as the base. So in this case, we need to explicitly resolve the URL on import.meta.url.

fixes #13770

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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