eac466d7bd
Salvage follow-up for PR #100269. The flag landed upstream in 0.3.x; binaries before it (e.g. 0.2.8, verified locally) fatally reject the flag with 'unknown argument', breaking every Browser Use launch. Probe 'lightpanda help' once per process and omit the flag when the binary predates it. Also soften the unverified concurrency claim in the _http_cache_dir docstring and tell docs readers to stop sessions before deleting the live sqlite cache.