Global system shortcut and quake terminal-like mode

### Feature summary

Add Global system shortcut and quake terminal-like mode

### What problem are you trying to solve?

Would love a configurable global system shortcut to quickly show/hide the GHCP app, with a setting to open it in "quake terminal" mode (ie spawning from the top or bottom of the screen, with a fixed width/height % of the screen).

This would allow faster multitasking, sending prompts to your agents, continue working on other stuff then making the app pop back up in the front when any interaction is needed.

### Proposed solution

- add a setting to configure a global system shortcut to show hide the app
- add a setting to configure GHCP app as a "quake terminal" mode, with subsetting: spawn from top or bottom (with animation)
* in quake mode, the window is docked to either top or bottom of the screen and always centered horizontally, with a separate size different than the regular window size: if you're resizing the quake window, it doesn't affect the regular GHCP window but any time you open the quake window it will have the size you set.
* in quake mode, when the GHCP quake window lose focus it's automatically hidden. Same if the global system shortcut for it is hit again
* the quake mode window is always spawning on the current active screen (the one having the focused window)
* the quake window is separate from the regular GHCP window and doesn't impact it in any way

### Workflow impact

Allow to always have your GHCP window at hand, regardless of which screens/apps are used, so you don't look for it. Enables faster workflows and task switching.

### Installation context

_No response_

### Additional context

_No response_

No files, tests, or implementation entry points are named. Start by locating the desktop window and settings code, then determine how global shortcuts, separate quake windows, screen selection, focus hiding, sizing, and animation are handled; done means these behaviors are configurable and work independently of the regular window.

Written by the indexing model from the issue text.