[shared] Move git signing key to systemConfig

hosts/desktop/home-manager/default.nix

@@ -9,6 +9,4 @@
     ./hyprpaper.nix
     ./settings.nix
   ];
-
-  programs.git.signing.key = "706F53DD087A91DE";
 }

hosts/nidaros/home-manager/default.nix

@@ -4,6 +4,4 @@
   imports = with lib.custom; [
     (relativeToBase "home-manager")
   ];
-
-  programs.git.signing.key = "4E323F914029E976";
 }

hosts/pi4/home-manager/default.nix

@@ -4,6 +4,4 @@
   imports = with lib.custom; [
     (relativeToBase "home-manager")
   ];
-
-  programs.git.signing.key = "E3FA0E995C0D0E5E";
 }

hosts/thinkpad/home-manager/default.nix

@@ -9,6 +9,4 @@
     ./hyprland
     ./zen
   ];
-
-  programs.git.signing.key = "848D71DE0590C199";
 }

shared/base/home-manager/development/git.nix

@@ -1,4 +1,9 @@
-{ pkgs, common, ... }:
+{
+  pkgs,
+  common,
+  systemConfig,
+  ...
+}:
 
 {
   home.packages = with pkgs; [
@@ -23,7 +28,10 @@
         p = "push";
       };
 
-      signing.signByDefault = true;
+      signing = {
+        signByDefault = true;
+        key = systemConfig.git.signing.key;
+      };
 
       extraConfig = {
         init.defaultBranch = "main";