fix: ghostty dock support and display fix

[damoun]

Provides a robust fix for Ghostty on Ubuntu:

1. Wraps Ghostty with GSK_RENDERER=gl to fix OpenGL context errors.
2. Creates a dedicated launcher script that sources Nix profiles to ensure GUI launches correctly find the environment.
3. Overrides the XDG desktop entry to use the launcher script with nixGL, enabling seamless dock launching.
4. Correctly handles the absolute path to tmux in the Ghostty configuration.