Fix CI build failure and add missing LICENSE files

Add "require" export condition to tailwind-preset for Node 18 CJS
compatibility (jiti resolution). Add LICENSE files to react,
tailwind-preset, and hex-background packages. Add license field to
showcase packages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/showcase/desktop/package.json

@@ -2,6 +2,7 @@
   "name": "@dangerousthings/showcase-desktop",
   "version": "0.0.0",
   "private": true,
+  "license": "MIT",
   "description": "Desktop showcase for the Dangerous Things design system",
   "author": {
     "name": "Dangerous Things",

packages/showcase/mobile/package.json

@@ -2,6 +2,7 @@
   "name": "@dangerousthings/showcase-mobile",
   "version": "0.0.0",
   "private": true,
+  "license": "MIT",
   "main": "./index.js",
   "scripts": {
     "start": "expo start",