[HigorMonteiro]

🎯 Problem

The Server.serve() signature includes an open_url parameter, but passing open_url=True currently does not open the browser. Instead, it only logs an error:
Use open_url_delay instead of open_url.

For developers and CLI tools using livereload, requiring an explicit delay in seconds (open_url_delay) when they simply want to open the browser on startup is unintuitive and breaks expectations.

💡 Solution

1. In livereload/server.py: If open_url=True and open_url_delay is None, default delay to 0 so the browser opens automatically upon startup.
2. Preserves 100% backward compatibility for users explicitly setting open_url_delay.
3. In livereload/cli.py: Added -b / --open-url flag.
4. Added unit test test_open_url_true_opens_browser in tests/test_server.py.

🧪 Verification

• pytest tests/test_server.py passes.
• Validated real-world usage in local projects with server.serve(..., open_url=True).