docs: add --headed flag to SKILL.md open parameters

[vivainio]

The --headed flag was missing from the skill documentation. Document that playwright-cli open runs headless by default and show how to pass --headed to get a visible browser window.

[dgozman]

@vivainio While --headed is handy for manual usage, I wonder is the usecase for the agent to run headed? Please share - that will help us improve not only the docs or skill, but the product as well.

[vivainio]

Headed mode is useful for monitoring the execution when developing a test suite, or just to get a quick feedback that something sensible is happening while agent is navigating the site. In this mode, you can move "step by step", chatting with the agent while you drill through your use case.

[dgozman]

@vivainio Could you please try playwright-cli show and give us feedback? It is designed for this exact usecase.

[vivainio]

@dgozman playwright-cli show didn't work properly. It opened a window with blank page saying "Not supported — v1.59.0-alpha-1771104257000".

[dgozman]

@vivainio I guess you have to update your versions of playwright-cli to make it work. Let us update the message to be more helpful.