feat: connect Fara to remote browsers over CDP

[Magnus Müller (MagMueller)]

What changed

• Add cdp_url support to the Fara 1.5 Playwright environment and the Fara-7B browser manager.
• Read FARA_CDP_URL in fara-cli and reject the ambiguous --browserbase + --cdp_url combination.
• Document the Browser Use Cloud create, connect, and stop flow.
• Cover existing-page and empty-context CDP connections.

Why

Both runners already use Playwright, and the BrowserBase path already connects over CDP. The CLI could not connect to another managed Chromium browser. This exposes that existing boundary without adding another provider SDK.

Checks

• pytest tests/test_remote_cdp.py tests/test_fara15.py -q (11 passed)
• Ruff format and lint on every changed Python file
• Built the sdist and wheel
• Ran real local CDP smoke tests for Fara 1.5 and Fara-7B
• Verified CLI help and the BrowserBase/CDP conflict guard

[Magnus Müller (MagMueller)]

@microsoft-github-policy-service agree company="Browser Use Inc."