Mission Control Space previews disappear while Hex is running on macOS 27 Beta

**Describing the bug**

When Hex is running, Mission Control no longer shows the open app windows inside the visible Desktop/Spaces previews.

The Spaces bar itself still appears, but the previews are empty, show only the wallpaper, or show a black preview, even though apps are open in those Spaces.

I confirmed that Hex is the trigger:

* If I quit Hex, Mission Control previews return to normal.
* If I launch Hex again, the Mission Control previews disappear again.

This seems similar to behavior caused by other transcription/overlay apps, where an invisible or always-on overlay window can interfere with macOS Mission Control.

**To Reproduce**

Steps to reproduce the behavior:

1. Launch Hex.
2. Open several apps across multiple macOS Desktop Spaces.
3. Open Mission Control.
4. Observe that the Desktop/Spaces previews do not show the open app windows.
5. Quit Hex.
6. Open Mission Control again.
7. Observe that the app-window previews return to normal.

**Expected behavior**

Hex should be able to keep running in the background and respond to the global hotkey without breaking Mission Control previews.

Ideally, Hex would not keep a persistent all-Spaces transparent overlay window active while idle. The overlay should only appear while recording/transcribing, or there should be a “headless / no persistent overlay” mode.

**Screenshots**

I attached a screenshot showing Mission Control where the Desktop/Spaces previews are visible, but the open app windows are missing while Hex is running.

**Desktop**

* Hex version: 0.7.6
* macOS: macOS 27 beta
* Mac: MacBook Pro M2 Pro / Apple Silicon
* Displays: single display & multiple displays

**Additional context**

I rely on Hex and would prefer to keep it running continuously. However, I do not necessarily need the overlay, Dock icon, or menu bar UI to be visible while idle.

Potential technical area to inspect:

* `InvisibleWindow` appears to create a transparent full-screen `NSPanel`.
* It uses all-Spaces style behavior such as joining Spaces / full-screen auxiliary behavior.
* `HexAppDelegate.presentMainView()` appears to create and order this invisible window during app launch.

My suspicion is that this persistent invisible panel may be confusing Mission Control on macOS 27.

Possible fixes could include:

* Create/order the invisible overlay only while recording or transcribing.
* Hide/order out the overlay when Hex is idle.
* Add a “headless / no persistent overlay” mode that keeps hotkeys and transcription working without a persistent all-Spaces window.
* Adjust the window collection behavior if the all-Spaces behavior is not required while idle.

Start by reading InvisibleWindow and HexAppDelegate.presentMainView() to understand when the transparent full-screen NSPanel is created, ordered, and assigned all-Spaces behavior. Reproduce the issue on macOS 27 beta with Hex 0.7.6, then verify that Mission Control previews remain visible while Hex stays running and global hotkeys and recording/transcription still work.

Written by the indexing model from the issue text.