Extract aerospace configuration into reusable modules

Create both home-manager and nix-darwin modules for aerospace window
manager configuration, removing 110+ lines of duplicated config from
machine-specific files.

Changes:
- Add home/modules/aerospace module with configurable leader key
- Add modules/aerospace.nix for system-level macOS settings
- Include autoraise configuration in home module
- Update home-darwin-work.nix to use new modules
- Update johno-macbookpro configuration to use system module
- Remove inline aerospace/autoraise config and launchd agents

machines/johno-macbookpro/configuration.nix

@@ -1,6 +1,10 @@
 { config, lib, pkgs, ... }:
 
 {
+  imports = [
+    ../../modules/aerospace.nix
+  ];
+
   # Basic system configuration for macOS work laptop
   system.stateVersion = 6;
 
@@ -12,13 +16,12 @@
     dock.autohide = true;
     finder.AppleShowAllExtensions = true;
     NSGlobalDomain.AppleShowAllExtensions = true;
+  };
 
-    # Configure spaces to span displays (required for aerospace multi-monitor support)
-    CustomUserPreferences = {
-      "com.apple.spaces" = {
-        spans-displays = true;
-      };
-    };
+  # Enable aerospace system settings
+  services.aerospace = {
+    enable = true;
+    enableSpansDisplays = true;  # Default, but shown for clarity
   };
 
   # TODO: Find a way to not duplicate this