Fix host comparison and use Tools::file_get_contents for image downloads

[CySSoO]

Motivation

• The webp conversion attempted remote downloads for same-host images due to an incorrect domain comparison, which produced HTTP failures and console errors.
• Using raw file_get_contents produced PHP warnings when remote fetches failed during image downloads.
• Resolving same-host URLs to local file paths avoids unnecessary network requests and potential service errors.
• Using the framework helper for fetching improves error handling and suppresses noisy warnings.

Description

• Extract the current host with parse_url(Tools::getHttpHost(true), PHP_URL_HOST) and fall back to Tools::getHttpHost(false) when necessary.
• Update the host comparison in urlToFilePath to compare parsedUrl['host'] against the extracted currentHost so same-host URLs are treated as local.
• Replace file_get_contents($url) with Tools::file_get_contents($url) in downloadImage to use the framework’s safer fetch helper.
• Ensure urlToFilePath returns a local filesystem path for same-host images and downloadImage returns false on download failure.

Testing

• No automated tests were run.

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Codex Task