Implement quick-terminal-screen for Linux/Wayland

[jguthmiller]

I like having a "quake" style quick terminal, and prefer to have it stick to my primary monitor. My setup is KDE Plasma, Wayland, and Debian Trixie. I searched existing discussions and issues and didn't find anything covering this, so I'm opening a new discussion. Since it solves a problem I have, I wanted to try implementing it myself. See main...jguthmiller:ghostty:quick-terminal-screen-linux.

The approach uses kde-output-order-v1 to discover the compositor's primary output, then matches its connector name against GDK's monitor list to pass to gtk_layer_set_monitor(). The monitor is re-resolved on every syncQuickTerminal call so config reloads and monitor changes take effect without restarting. When the protocol isn't available (e.g., GNOME, sway), it falls back to the first monitor reported by GDK.

Tested on KDE Plasma 6 with multiple monitors. I confirmed the quick terminal pins to the primary and falls back correctly on a single-monitor setup.

Related: #8076 (request to fix quick terminal to a specific display) and possibly #10247 (sizing issues when switching between monitors of different resolutions).

Note: AI-assisted implementation (Claude Code and Codex). I did the research and planning, and verified all changes manually on my setup. I've been writing software and using Linux for 20 years, so I have a decent grasp on the concepts and the changes I've made.

Please let me know if you have any questions or feedback!

[pluiedev]

There are some problems with the implementation (spotted a stale reference to a stack variable at a first glance, in fact) but the idea itself seems to be sound. Please spend some extra time cleaning up the code and especially the state management, and then make a PR whenever you deem it ready - just link this discussion so that people don't mistake this for an unapproved drive-by.

[jguthmiller]

Will do. Thanks for taking the time to look at it!