Token Budget

Token budget management and allocation.

Token budget management for fair resource allocation across projects.

BudgetManager calculates target token ratios from per-project credit weights and tracks how far each project's actual usage deviates from its target (the "deficit score"). The Scheduler uses these deficit scores to decide which project should receive the next available agent -- the most under-served project wins.

This keeps agent time proportional to credit weights over rolling windows, even when projects have bursty workloads.

See specs/scheduler-and-budget.md for the full specification.