Description
This PR updates the push() method to return the unique job ID of the queued job instead of a simple bool. This allows consumers to track jobs based on their identifier.

• Queue::push() now returns a string (job ID) on success or null on failure
• Method signature updated from bool to ?string
• This is a breaking change in method behavior

Closes #61

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide