Replace insecure URL validation regex with proper URL constructor validation

[Copilot]

The prework link validation used a permissive regex /^https?:\/\/.+/ that could allow malicious URLs to pass validation.

Changes Made

• Security: Replace regex pattern with isValidUrl() function that uses JavaScript URL constructor
• Import: Add isValidUrl import from existing @utils/formValidations
• Validation: Update prework link field to use validate property instead of pattern

Code Changes

// Before - insecure regex validation
pattern: {
    value: /^https?:\/\/.+/,
    message: "Please enter a valid URL (starting with http:// or https://)",
}

// After - secure URL constructor validation
validate: (value) => {
    if (!isValidUrl(value)) {
        return "Please enter a valid URL (starting with http:// or https://)";
    }
    return true;
}

The isValidUrl() function leverages the browser's native URL constructor for robust validation that prevents malformed and potentially malicious URLs while maintaining the same user experience.

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