✨(demo) add app demo

This demo is useful to test in the real usage of the design system as a real
user that will generate its own customized design tokens, implements the design
system's components, etc ...

apps/demo/cunningham.cjs

@@ -0,0 +1,7 @@
+module.exports = {
+  theme: {
+    colors: {
+      primary: 'purple'
+    },
+  },
+};