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>

docs/CUSTOMIZATION.md

@@ -31,6 +31,10 @@ Your configuration lives in `~/.config/nomarchy/config.nix`:
   # Performance (security tradeoff!)
   enableMitigationsOff = false;
 
+  # Boot
+  bootloader = "systemd-boot";  # or "limine" for prettier boot
+  enablePlymouth = false;       # Boot splash screen
+
   # Theme
   theme = "classical";
 }