Fix translations.json fetch path for subfolder installations

[Copilot]

When REDAXO is installed in a subfolder, the hardcoded absolute path /assets/addons/vidstack/translations.json resolves against the server root rather than the installation base, producing a 404.

Change

Derive the translations.json URL dynamically from document.currentScript.src at script parse time, using the standard URL constructor to resolve the sibling file correctly regardless of install path:

const translationsUrl = document.currentScript?.src
    ? new URL('translations.json', document.currentScript.src).href
    : '/assets/addons/vidstack/translations.json';

This naturally handles ?buster=… query strings on the script URL and falls back to the previous absolute path if currentScript is unavailable.

[TobiasKrais]

Tested and works