Handle CORS errors in form submissions with fallback to full page redirect

[Copilot]

When forms redirect to external URLs without CORS headers, XMLHttpRequest.send() throws instead of gracefully degrading. This breaks legitimate use cases like redirecting to external authentication providers or payment gateways.

Changes:

• Wrap request.send() calls in try-catch blocks to intercept CORS exceptions
• Fall back to window.location.href redirect when AJAX fails
• Handle both file upload and standard form submission paths
• Introduce requestUrl variable to track the correct redirect target for GET (with query params) vs POST requests

Implementation:

try {
    request.send(parameters.join('&'));
} catch (e) {
    // CORS error - fall back to full page redirect
    window.location.href = requestUrl;
}

The change is transparent to same-origin requests while enabling external redirects that previously failed with console errors.

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