Add a read-only Browser Use durable cookbook

[MagMueller]

Adds a read-only Browser Use cookbook for #91. Each completed page read is saved as JSON; after a killed process, a new process reads only unfinished pages.

Includes demo/live modes and restart tests. Browser sessions, agent memory and external actions are out of scope. This is a partial implementation, not a fix for all of #91.

[sdageltc]

Hey @MagMueller! 👋

Thanks for contributing this cookbook for #91!

I pulled and verified your branch locally:

• ✅ Unit & integration tests passing (pytest tests/test_browser_use_cookbook.py)
• ✅ Real process death and restart verification passed ( est_sigkill_then_fresh_process_skips_first_read)
• ✅ Code formatting & linting 100% clean (
  uff check .)
• ✅ Clean fallback between --demo and --live mode with proper @durable_async step scoping

Whenever you are ready to mark this PR as Ready for Review, let us know and we will merge it into main and acknowledge your contribution in our .all-contributorsrc and README! 🚀