fix: use correct publicDir in ERR_LOAD_PUBLIC_URL

[appsforartists]

Description

Failed to load url /config.js (resolved id: /config.js). This file is in /public and will be copied 
as-is during build without going through the plugin transforms, and therefore should not be 
imported from source code. It can only be referenced via HTML tags.

had a hardcoded value for /public. This introspects the correct value from config to improve the error message.

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the PR Title Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.
  • There don't seem to be any tests for the error message, and I don't know the repo well enough to make one.

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[bluwy]

Thanks!