Add Limine bootloader support with themed styling

Phase 2: Bootloader improvements

- Add bootloader choice: systemd-boot (default) or Limine
- Configure Limine with classical theme colors:
  - Dark brown background (#1a1611)
  - Tan text (#d4c4a8)
  - Gold accents (#d4a857)
- Add Plymouth boot splash option
- Update installer to prompt for bootloader choice
- Add example-limine configuration
- Update documentation with boot options

Users can now choose between:
1. systemd-boot - Simple, reliable, well-tested (default)
2. Limine - Modern, prettier, themed to match Nomarchy

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.nix

@@ -57,14 +57,17 @@
       # Performance (security-conscious defaults)
       enableMitigationsOff = false; # Opt-in only
 
+      # Boot
+      bootloader = "systemd-boot"; # or "limine"
+      enablePlymouth = false; # Boot splash
+
       # Theme
       theme = "classical";
     };
   in {
     # NixOS configurations
     nixosConfigurations = {
-      # Example configuration (requires hardware-configuration.nix)
-      # Users create their own configuration via the installer
+      # Example configuration with systemd-boot (default)
       example = mkHost {
         system = "x86_64-linux";
         config = defaultConfig // {
@@ -73,7 +76,24 @@
         extraModules = [
           # Minimal test hardware config
           ({...}: {
-            boot.loader.systemd-boot.enable = true;
+            fileSystems."/" = {
+              device = "/dev/disk/by-label/nixos";
+              fsType = "ext4";
+            };
+          })
+        ];
+      };
+
+      # Example configuration with Limine bootloader
+      example-limine = mkHost {
+        system = "x86_64-linux";
+        config = defaultConfig // {
+          hostname = "nomarchy-limine";
+          bootloader = "limine";
+          enablePlymouth = true;
+        };
+        extraModules = [
+          ({...}: {
             fileSystems."/" = {
               device = "/dev/disk/by-label/nixos";
               fsType = "ext4";