Fail with RuntimeError when WEB_CONCURRENCY or BANGUI_WORKERS > 1.
In-memory session cache, rate-limit windows, and runtime state are
process-local. Multi-worker silently causes stale limits, ghost sessions,
inconsistent status.
Skipped when TESTING=1.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>