Make sure concurrency stays at `minConcurrency` while the system is overloaded

crawlee-python was freezing after an overload: its AutoscaledPool dropped to zero concurrency instead of keeping min_concurrency tasks running. Fixed in apify/crawlee-python#2235.

JS has the same guard in ConcurrencySystem.hasCapacityForTask() (packages/basic-crawler/src/internals/autoscaling/concurrency_system.ts), which refuses on overload only once currentConcurrency >= minConcurrency. Worth checking that it really behaves that way in v4 before it ships, since the budget now lives in a governor that several pools can share. Pin it with a test once confirmed.

✍️ Drafted by Claude Code