Policy: leaving a match after accepting (two-tier consequences)

**Status: needs triage** (policy / enhancement)

## Summary
Once a player accepts a match (Balatro-Multiplayer/BalatroMultiplayer#493), they may still need to leave. Consequences should depend on **when**:

- **Leaving after the run has started** → treated as a **normal loss** (full game loss + MMR loss), same as any forfeit mid-game.
- **Leaving during the ban phase** (before the run starts) → **some MMR loss but no game loss**, plus possibly a **queue-time penalty**. Bailing during bans is lighter than abandoning a live game, but shouldn't be free.

## Open questions
- How much MMR the ban-phase leave costs (fixed amount vs fraction of a loss).
- Size of the queue-time penalty, and whether it escalates on repeat.
- Exact boundary for "run started" (first blind? deck locked in?).

先阅读引用的对局接受 issue：Balatro-Multiplayer/BalatroMultiplayer#493，并追踪接受后当前是如何处理退出的。这里没有指定文件、测试或入口点。在确定实现范围之前，需要先就 run 开始的边界、ban 阶段的 MMR 损失以及排队时间惩罚达成一致，才算完成。

由索引模型根据 Issue 内容生成。