Add Patchright browser backend

Add Patchright as an optional alternative browser backend alongside Playwright.

Patchright could be useful for sites that block or behave differently with normal browser automation.

Start by locating the existing Playwright browser backend and the entry point used to select or configure browser backends. Read how optional dependencies are handled, then verify that Patchright can be selected as an alternative without changing the existing Playwright path and that the CLI works with either backend.

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