Per-level token/turn budgets: task -> intent (worker run) -> planner round
(counted inside the task). A child's effective budget is
min(own budget, parent's remaining above the wrap-up reserve). When the task
can no longer afford one worker, workers stop claiming intents and the task
settles through one forced wrap-up planner round (the existing settle
sequence, budget words instead of the timeout words).
Config: ARTEX_TASK_BUDGET_TOKENS, ARTEX_TASK_BUDGET_TURNS,
ARTEX_INTENT_BUDGET_TOKENS, ARTEX_INTENT_BUDGET_TURNS. 0 or unset = unlimited;
with all four unset nothing changes.
