feat(branding): professionalize installer and system branding

- Refactor installer with Gum for a professional interactive experience
- Create custom Nomarchy Plymouth theme with centered logo
- Establish assets/branding directory for official logos and ASCII art
- Update Fastfetch config with official ASCII art and declarative stats
- Declaratively link branding assets via Home Manager

assets/plymouth/nomarchy.script

@@ -0,0 +1,21 @@
+logo_image = Image("logo.png");
+
+screen_width = Window.GetWidth();
+screen_height = Window.GetHeight();
+
+logo_width = logo_image.GetWidth();
+logo_height = logo_image.GetHeight();
+
+logo_x = screen_width / 2 - logo_width / 2;
+logo_y = screen_height / 2 - logo_height / 2;
+
+logo_sprite = Sprite(logo_image);
+logo_sprite.SetX(logo_x);
+logo_sprite.SetY(logo_y);
+logo_sprite.SetOpacity(1);
+
+fun refresh_callback () {
+  # Simple rotation or pulse could go here
+}
+
+Plymouth.SetRefreshFunction (refresh_callback);