Usage icon registers hover events and presents tooltip when chat window is hidden

**Describe the bug**
The `usage icon` registers hover events and presents the tooltip when chat window is invisible (on initial launch of Xcode) and when chat window is hidden (minimised). The `usage icon` tooltip is present anytime you hover where the window _would_ be even when window is not currently visible, or another applications window is on _top_ of the chat window.

**Usage icon tooltip:**
> Copilot Business Plan
> You have no monthly limit on Al credits usage set by your organization. [{github-copilot-settings link}](https://aka.ms/github-copilot-settings)

**Versions**
- MacOS 15.6.1 (24G90)
- Xcode 26.3 (17C529)
- GitHub Copilot for Xcode (0.50.0)

**Steps to reproduce**
1. Launch Xcode
2. Hover where icon would be*, tooltip is presented
3. Open chat from MacOS menu bar
4. Hide chat window
5. Hover where icon would be, usage tooltip is presented

\* chat window pane typically launched on right hand side, but can be hard to figure out since you can't see the window, steps 3-5 alone still replicate the issue.

**Screenshots**
Chat window is active (standard behaviour)

Xcode window is active, chat window not visible

Chat window not visible, no other windows over where chat window would be if visible

All windows are hidden (minimised)

**Logs**
N/A?

**Additional context**
Doesn't matter whether other widows are active on top of where chat window would be while hidden. All windows can be hidden and usage icon tooltip is always displayed when hovering on the spot where icon is in the window. Might be due to work managed Macbook M3 Pro, haven't tested on my personal Mac Mini M4.

Start by reproducing the usage icon hover behavior on macOS with the chat window visible, hidden, minimized, and covered by another window. Inspect the usage icon's hover and tooltip handling together with chat-window visibility; done means the tooltip appears only when the chat window is visible, while the listed reproduction steps no longer trigger it when hidden.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.