Cost Budget Check

This is the gatekeeper that actually enforces the four-tier budget alert ladder (50/75/90/100%) that was documented but never checked until now. It reads your cost tracking data, calculates spend against your configured budget limit, and tells you whether you're at INFO, WARNING, CRITICAL, or HARD_STOP. Run it after every cost-track session or before spawning expensive agent swarms. The HARD_STOP level exits with code 1, so you can gate critical operations with a simple check && spawn pattern. Honestly, if you're running any kind of autonomous agent workload with real budget constraints, this should be in your monitoring loop.