Generalize the GROK-only _grok_spawn_parked guard to _provider_spawn_parked.
spawn_agent now consults the RateLimitStateTracker for every provider, so
Anthropic session/overload parking suppresses container launches instead of
letting the dispatcher re-spawn every tick. Fail-open on tracker errors.
- Rename _grok_spawn_parked -> _provider_spawn_parked (any provider)
- Update spawn_agent log + gate
- Update grok-rate-limit tests to cover general provider behavior