Track running token usage against goal's `token_budget`, surface at 50/80/100% thresholds, stop at 100%.
USE WHEN: `goal-persistence` active AND user provided `token_budget`, user said "do X within Y tokens" / "用 Y token 完成" / "不要超预算" / "stayed within budget" / "超出预算" / "用了多少 token", about to start sub-task and need to know remaining budget, at every compact / turn boundary.
TRIGGER PHRASES: "token budget", "预算", "Y tokens", "不要超过", "stayed within budget", "超出预算", "用完没", "用了多少 token", "预算跟踪", "50% / 80% / 100%", "token 预算".
SKIP WHEN: goal has no budget (user did not set one), user explicitly said "no budget tracking for this one".
