Feature request: Show additional usage budget in the app

Feature request: Show additional usage budget in the app

When my included AI token allowance is exhausted and usage switches to my **Additional usage** budget, there’s no in-app way to see how much I’ve used, how much remains, or what my limit is. I have to leave the app and visit the website to find this information, which is inconvenient and makes it difficult to monitor spending while working.

Please add an in-app usage view that shows:

- Additional usage consumed
- Remaining budget or current limit
- Billing period or reset date
- A link to manage or adjust the budget

This would make usage and spending much more transparent and provide a smoother experience for users who rely on additional usage.

---
| Field | Value |
| --- | --- |
| App version | 1.1.12 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 7 |

从应用的 /chat 体验开始，追踪 included AI token usage 和现有网站 billing link 的展示方式。确定可以从哪里获取并展示额外的 usage data、limits、reset dates 和 budget-management links。完成标准是应用内视图显示已消耗的 usage、剩余或最大 budget、billing period 或 reset date，以及一个 management link。

由索引模型根据 Issue 内容生成。