- Fix ActError with 0 steps executed in execute_instruction
- Apply same thread-safe pattern as inspect_browser fix
- Add async wrapper for nova.act() calls in execute_browser_task_with_nova_async()
- Update browser_control.py to use direct async calls instead of double-threading
- Remove @pytest.mark.xfail markers that masked real threading issues
- Comprehensive testing confirms fix works with complex sites like HackerNews

Resolves Linear STR-38: execute_instruction ActError in production

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Co-Authored-By: Claude <noreply@anthropic.com>