feat: add global theme mode and Yazi shortcut

- Added theme.mode to config.nix for global dark/light mode control.
- Updated Matugen to apply GTK dark mode preferences based on the global theme.
- Added a Hyprland bind (SUPER+X) to launch Yazi via uwsm.

config.nix

@@ -16,6 +16,9 @@
         email = "kenji@hakase";
         defaultBranch = "master";
       };
+      theme = {
+        mode = "dark";
+      };
       terminal = {
         default = "ghostty";
         font = "MonoLisa";
@@ -74,6 +77,9 @@
         email = "kenji@macbook";
         defaultBranch = "master";
       };
+      theme = {
+        mode = "dark";
+      };
       terminal = {
         default = "ghostty";
         font = "MonoLisa";